DE102024106171B4 - Semiconductor laser with semiconductor material system with Fermi level control by doping the active region at spatially indirect transitions - Google Patents

Abstract

Semiconductor laser with semiconductor material systems of elements for a semiconductor, comprising
a substrate region (12) which is a substrate made of at least one carrier material, and
at least one active region (20) with three sub-regions (30);
a separation region (14) which is a barrier between the substrate region (12) and the active region (20), or between several repetitions of active regions (20), between sub-regions (30) of an active region (20) or between the active region (20) and the interface with the air;
where
the first active sub-region (32) is a doping region and comprises a semiconductor material system comprising at least one element and a doping;
the second active sub-region (34) is a doping region and has a doping and a further semiconductor material system comprising at least one element which differs from the semiconductor material system of the first active sub-region (32);
the third active sub-region (36) is a doping region and comprises the semiconductor material system of the first active sub-region (32); and
the active region (20) of the semiconductor laser (10) has a doped W structure; and
at least one of the semiconductor material systems in the second active sub-region (34) and/or in the first active and third active sub-region (32, 36) is doped such that the band gap in the W structure can be adjusted in a predetermined manner such that the emission energy of the semiconductor laser (10) can be adjusted for emission energies smaller than the transition energies of the individual sub-regions (30); and
at least one element of the semiconductor material system of the second active sub-region (34) comprises at least one element semiconductor and a doping.

Description

The present invention relates to a semiconductor laser with a semiconductor material system of elements for a semiconductor comprising a substrate region, an active region and a separation region which is a barrier between the substrate region and the active region.

Semiconductor lasers are widely used in industry and in end-user devices. They are used in many areas, from data transmission to sensor technology and medical technology. Although the requirements profile for lasers is very different and the properties of the lasers used vary greatly, there are three essential characteristics that can be used to improve and optimize known laser technologies.

Firstly, different areas of application require different emission energies, which cannot currently be achieved with conventional semiconductor lasers. Secondly, higher energy efficiency is an important property that will become even more important in the future. The third aspect concerns the sustainability of the raw materials used. This applies both to the type of elements used for the semiconductor laser and to the quantities used and used, or to the complexity of the manufacturing process, in which large amounts of waste must be significantly reduced in the future.

Currently, semiconductor lasers mainly use spatially direct transitions in semiconductor material systems as the active medium. The emission energy can be varied by the band gap of the active material, by strain and by quantization effects such as the dimensionality of the active material, layer or material thicknesses and barrier material and thus barrier energy. A spatially direct transition between the valence band edge and the conduction band edge is therefore crucial for the transition energy. These parameters are dependent on one another. For example, the change in the band gap generally also results in a lattice mismatch. For different spectral ranges, different multinary material systems are used as multiple quantum films in complex heterostructures. For example, materials that can be used are (Ga,In)(N,As,P) for the near-infrared spectral range or (Ga,In) in combination with nitrogen (N) for blue and green laser diodes.

Other possibilities are quantum cascade structures, in which cascades of typically quantized intersubband transitions are used in complex multiple quantum structures. Here, the optical transitions between individual, typically higher states take place within quantized layers. The band gap energies between valence and conduction band edges for quantum cascade structures are typically far removed from the energies of the optical transitions used for laser activity and can therefore be considered irrelevant.

Furthermore, so-called W structures made of undoped type II heterostructures are used. Such lasers offer the advantage over conventional type I lasers and quantum cascade lasers that losses due to intersubband scattering and Auger losses can be strongly suppressed. Here, the energy of the optical transitions of type II is relevant for the laser activity, which is determined by the combination of the intrinsic materials.

So far, multinary heterostructures have been used to achieve different emission energies. In addition to different material compositions, different material systems are also used. In W structures, the intrinsic hetero-offsets of the material combinations were used at the type II transitions.

The undoped type II structures frequently used in the state of the art have only very limited options for setting the target wavelengths. This is due to the limitation of the required good structural quality and the associated epitaxial growth of intrinsic layers. The emission wavelengths in currently used semiconductor lasers are therefore essentially determined for all laser types by the material and the layer thickness of the active layer. Furthermore, defects arise that reduce efficiency or do not allow efficient laser operation at all. These effects are caused by intrinsic lattice mismatches in multinary layer systems on available substrate materials, such as gallium arsenide (GaAs), indium phosphide (InP), sapphire, silicon carbide (SiC) or silicon (Si). Furthermore, the epitaxial growth of such partially quinternary layers is extremely complex and time-consuming. This means that some emission energies are very difficult or even impossible to achieve. Accordingly, inefficient components must be used.

In addition, in order to achieve particularly low emission energies, it is necessary to use sustainable substrate platforms in production. The same applies to quantum cascade structures. Here, the structural mismatch is also very critical, since in the partially The many hundreds of epitaxial layers required lead to lattice defects, which inevitably lead to the functional failure of semiconductor lasers.

The published patent applications US 2015/0244144 A1 , US 5,799,026 A , DE 10 2011 103 143 A1 , EP 3 506 439 A1 , US 6,154,475 A , US 2007/0051963 A1 and US 2012/0269221 A1 be seen.

The task is therefore to propose an improved semiconductor laser with semiconductor material systems.

The present object is achieved by a semiconductor laser having the features of claim 1.

The invention thus relates to a semiconductor laser with a semiconductor material system made of elements for a semiconductor. The semiconductor laser comprises a substrate region, which is a substrate made of at least one carrier material, and at least one active region with three sub-regions and a separation region. The separation region is a barrier between the substrate region and the active region, between several repetitions of active regions, between sub-regions of an active region or between the active region and the interface with the air. The repetitions of the active regions lead to an increase in the gain amplitude and thus to greater amplification. This increase should ideally be linear with the number of repetitions.

The first active sub-region is a doping region and has a semiconductor material system made up of at least one element in addition to the doping. The second active sub-region is a doping region and has a semiconductor material system made up of at least one element in addition to the doping that differs from the semiconductor material system of the first active sub-region. The third active sub-region is a doping region and has the semiconductor material system of the first active sub-region. The material systems of the first and third active sub-regions are thus the same.

The active region of the semiconductor laser is a doped W structure. At least one of the semiconductor material systems in the second active sub-region and/or in the first and third active sub-regions is doped in such a way that a band gap in the W structure can be set in a controlled manner in a predetermined manner such that the emission energy of the semiconductor laser can be set for emission energies smaller than the transition energy of the individual sub-regions.

The invention thus relates to a concept for the design of semiconductor laser structures and a semiconductor laser. The invention is based on the basic idea of controlling the emission energy of a spatially indirect transition, so-called type II transition, of two or three semiconductor material systems by means of doping. All known doping concepts are conceivable. In particular, homogeneous doping or delta doping can be used. In addition to the band gap energies of the semiconductors used in the active layer, the band discontinuity at the interface is particularly important for the emission energy of a type II transition. The interface is also referred to as the band offset. Since the charge carriers recombine from the conduction band of one semiconductor into the valence band of the other, the energy difference between the conduction band of one semiconductor and the valence band of the other is crucial for the emission of the laser. This band discontinuity is determined to a first approximation by the exit energies and the Fermi level of the semiconductor heterostructure. The doping determines the relative position of the valence and conduction band edges of all semiconductors relative to the Fermi level. The Fermi level is constant for the semiconductor heterostructures without bias.

The relative position of the valence and conduction band edges of the individual semiconductors in the active region is achieved by controlling the Fermi level through doping. This allows the transition energy of the optical transitions to be controlled. The doping thus determines the conductivity of the element or compound semiconductors. In addition, the doping determines the energetic position of the valence and conduction band levels of individual layers of element or compound semiconductors. However, since the Fermi level of a heterostructure, such as the W structure intended here, is continuous, the doping also controls the energy of spatially indirect transitions at heterointerfaces, which is responsible for the laser transitions in these W structures, and can therefore be adjusted by doping.

In the context of the invention, a semiconductor material system comprising elements for a semiconductor is understood to mean that the elements do not necessarily have to be semiconductor materials or elements or semiconducting elements themselves, but can also comprise metals, gases and other chemical elements or molecules that are suitable, e.g. in combination with other elements, to be part of a semiconductor material system or to build such a system or to be a material for a semiconductor laser.

In a preferred embodiment, the second active sub-region has a different doping as the first active sub-region and the third active sub-region. For example, a possible material system could be formed from phosphorus and nitrogen plus nitrogen and gallium arsenide (PN+N GaAs). Various dopings are possible here, such as Be, C, Mg, Si, Ca, Ge, Zn, Se, Te. It is therefore also possible that the second active sub-region is undoped, the first and third active sub-regions are doped or vice versa.

According to the invention, at least one element of the semiconductor material system of the second active sub-region comprises at least one element semiconductor and a doping. The element semiconductor is particularly preferably from the fourth main group of the periodic table of elements PSE. For example, germanium (Ge) or silicon (Si) could be used. A possible structure of an active region could consist of the materials GaN-Ge-GaN, with the second active sub-region comprising germanium (Ge).

A preferred embodiment of the semiconductor laser is characterized in that at least one element of the semiconductor material system of the first active sub-region and the third active sub-region comprises a metal alloy. In a preferred embodiment, the alloy is made of metal that belongs to the third or fifth main group of the PSE. The first active sub-region and the third active sub-region most preferably have different dopings. A preferred embodiment can be such that the first and third active sub-regions comprise a doping of aluminum, gallium and arsenide ((Al,Ga)As) and the second active sub-region comprises, for example, the elements gallium (Ga) and arsenic (As-). These layers are preferably doped in accordance with the above statements. Other combinations could be, for example: GaN/Ge/GaN; GaN/Si/GaN; GaN/SiGe/GaN. Here, the compound semiconductors of the first and third active sub-regions are doped in accordance with the above statements; The second active subregion, which consists of elements of the fourth main group, is doped with elements of the third or fifth main group.

In a further preferred embodiment of the semiconductor laser, the semiconductor material system of the first active sub-region and the third active sub-region comprises alloys of metal. Metals from the third or fifth main group of the PSE are particularly preferred. The alloys and/or dopings are particularly preferably different.

According to a likewise preferred embodiment of the semiconductor laser, at least one of the active sub-regions comprises a semiconductor material system made of at least one metal and/or one gas, preferably of metal and gas. This applies under typical growth conditions for pressure and temperature. Preferably, the other active sub-region(s) are formed from an alloy semiconductor with at least one semiconductor material. Typical examples are a composition of the active region such that the first and third active sub-regions comprise the elements gallium (Ga) and nitrogen (N), while the second active sub-region has the element germanium (Ge). Another example provides silicon (Si) in the second active sub-region, while the first and third active sub-regions also comprise the elements gallium (Ga) and/or nitrogen (N). The individual active sub-regions are doped according to the above statements in order to adjust the valence and conduction band offsets by controlling the Fermi level so that the desired transition energy of the laser transition in the W structure is achieved. A further embodiment can consist in the second active sub-region comprising the elements silicon (Si) and germanium (Ge). Here, doping preferably takes place using one or more elements from the third or fifth main group, such as boron, P or As.

In a preferred embodiment of the semiconductor laser, the first active sub-region and the third active sub-region are each a semiconductor material system that comprises two different elements made of semiconductor materials. Both elements of the semiconductor material system are also semiconductor materials, for example silicon (Si) and germanium (Ge). One possible structure of the active region provides that the first and third active sub-regions comprise silicon (Si) and germanium (Ge), while the second active sub-region has the elements gallium (Ga) and nitrogen (N). The doping of the individual active sub-regions takes place according to the above statements in order to achieve the desired transition energy of the laser transition in the W structure.

In a preferred embodiment of the semiconductor laser, it is designed such that the first active sub-region and the third active sub-region each have a greater width than the second active sub-region. In a preferred embodiment, the width of the first active sub-region and the third active sub-region are each at least 1.5 times as large as the width of the second active sub-region.

In a further preferred embodiment of the semiconductor laser, the semiconductor material system in the second active sub-region comprises an indirect semiconductor, which may be doped. The semiconductor The conductor material system in the first and third active sub-region is a direct semiconductor, which can also be doped.

A further preferred embodiment provides that the semiconductor material system in the second active sub-region is a direct semiconductor, which can be doped, while the semiconductor material system in the first and third active sub-regions is an indirect semiconductor, which can also be doped. For example, the active region can be designed such that the first and third active sub-regions comprise germanium (Ge), while the second active sub-region comprises the elements gallium (Ga) and nitrogen (N), wherein preferably all materials are doped in accordance with the above statements in order to achieve the desired transition energy of the laser transition in the W structure.

The dopings described in the subclaims can be selected such that they amount to at most 10%, preferably at most 7%, more preferably at most 5%, more preferably at most 3%, very preferably at most 2%. Dopings of at most 1% or less than 1% or very much less than 1%, for example less than 0.1% or less than 0.01%, are particularly preferred.

By means of suitable doping, the offset in germanium (Ge), for example, can be controlled well, robustly and reliably, for example in order to significantly change the W junction. In this way, p-type or n-type semiconductors can be produced. For example, GaAs could be doped with germanium (Ge), i.e. GaAs:Ge, preferably with a doping of <1% or better <<1% Ge. In the same way, germanium could also be doped with arsenide (As), i.e. Ge:As, or with boron (B), i.e. Ge:B, or also with gallium, i.e. Ge:Ga, or with antimony (Sb), i.e. Ge:Sb. Here the doping is also less than 1% or very much less than 1% (< 0.1% to < 0.01%).

• 1a bis 1d eine Prinzipskizze eines erfindungsgemäßen Halbleiters;
• 2 eine Prinzipskizze einer Modifikation; und
• 3 eine Prinzipskizze eines Oberflächenemitters

An embodiment of the invention is described below with reference to the accompanying drawings.

• 1a to 1d a schematic diagram of a semiconductor according to the invention;
• 2 a schematic diagram of a modification; and
• 3 a schematic diagram of a surface emitter

In the 1a to 1d Energy levels for different semiconductor lasers 10 are shown, with the conduction band and the valence band being shown in each case.

The laser transitions are controlled by doping the individual semiconductor materials. This doping controls the relative position of their valence and conduction band edges relative to the Fermi level 11, which is constant throughout the heterostructure.

The semiconductor lasers 10 comprise a substrate region 12, which is formed from a substrate with at least one carrier material, wherein in the embodiments shown here a separation region 14 is integrated to such an extent that a combined substrate region 12 with separation region 14 is shown. This region is referred to below in the figures as substrate region 12.

The substrate region 12 is followed by an active region 20 which comprises several sub-regions 30.

According to 1a the active region 20 comprises three sub-regions 30, a first sub-region 32, a second sub-region 34 and a third sub-region 36. The three sub-regions 30 are arranged in a W structure. Between the individual sub-regions 30 there is a separation region 14, which in the embodiment shown here is a gallium arsenide barrier (GaAs barrier). The substrate region 12 also comprises the elements gallium and arsenide.

The active region 20 is again followed by a barrier 40, which can be formed either from a separation region 14, a combination of separation region 14 and substrate region 12, or from a barrier region with several regions. The barrier region can also comprise, among other things, a separation region 14. In the embodiment shown here, the barrier comprises three adjacent regions, for example made of GaAs, Ga(As,P) and GaAs. Such barriers or similar barriers are known in the prior art.

An active region can in turn be connected to the barrier. In the semiconductor laser 10, several active regions 20 separated by a barrier 40 can be arranged in a row. In this case, a substrate region 12 can be provided at the end instead of a barrier.

The first sub-region 32 and the third sub-region 36 are constructed in the same way, as shown in this embodiment. They comprise the same materials. All three sub-regions 30 of the active region 20 are doped. The first sub-region 32 and the third sub-region 36 comprise a combination of gallium with an alloy using indium (Ga _0.95 and In _0.05 ) in combination with arsenide (As). This region can be undoped, as shown in this Realization (semi-insulating, si), or doped to shift the valence and conduction bands relative to the Fermi level. The second sub-region 34 is also doped and also includes the elements gallium (Ga) and arsenide (As), where arsenide has a 7% alloy using antimony (Sb). In the example shown here, the antimony doping is 7%, so that the material system of the second sub-region 34 is formed from GaAs _0.93 Sb _0.07 . This layer is doped by adding appropriate elements such as Zn or Te p or n in order to control the energy of the type II band discontinuities, which determine the laser energy of the W structure.

The doping and alloying of the sub-ranges 30 can vary. For example, it is possible and quite advantageous if the alloy using antimony Sb is in the range between 5% and 10%, for example about 9%.

Based on the 1a An example of the spatial extent of the individual sub-regions 30 and separation regions 14 can also be given. In the example provided, the separation regions can be approximately 1 nm wide, while the second sub-region 34 is 4 nm wide and the two outer sub-regions, i.e. the first sub-region 32 and the third sub-region 36, can each be 6 nm wide.

1b shows an embodiment of a doped W structure with intermediate GaAs barriers. The semiconductor laser 10 is based on a (Ga,In)As/Ga(As,Sb)/(Ga,In)As material system in W structure. In the embodiment shown here, the separation regions 14 between the sub-regions 30 of the active region 20 are δ-doped. The doping from the 1 nm GaAs layers of the separation regions serves as δ-doping, for example for the material system of the second sub-region 34 of the semiconductor laser in p-type. Consequently, for example, a GaAs _0.93 Sb _0.07 with δ-doping in p-type is provided.

The embodiment according to 1c is an example of a doped W structure of a semiconductor laser 10 without an intermediate GaAs separation region 14 between the sub-regions 30. This semiconductor laser also has a (Ga,In)As/Ga(As,Sb)/(Ga,In)As-W structure. In some application areas, this embodiment could have the disadvantage that the "Sb well" may not be seen in absorption.

The emission energy is crucial for the wavelength emitted and radiated by the semiconductor laser 10. This corresponds to a first approximation to the band gap that is formed between the valence band of the second sub-region 34 and the conduction band of the first sub-region 32 or third sub-region 36. This band gap can be influenced by suitable doping of the elements of the material system of the semiconductor laser and by suitable selection of the corresponding elements of the material system, which offers the possibility of adjusting the emission energy and the wavelength of the semiconductor laser in the desired form.

1d shows an example of a semiconductor laser 10 with a doped Si/GaN/Si-W structure. While the upper line 100 indicates the vacuum level in the energy scheme shown, the reference numeral 110 designates the conduction band of the gamma-like valence band states of the silicon. The reference numeral 120 designates the conduction band of the L-like conduction band minimum of the silicon or GaN. The reference numeral 130 designates the valence band of the gamma-like valence band state of the silicon or GaN. The numerical data of the band gap distances in 1d are in eV. Transitions between the individual bands are therefore marked in eV.

In the embodiment shown, the relevant transition between the gamma-like valence band states of silicon and the conduction band states in the natively n-doped GaN takes place. A variation of the n-doping in GaN determines the hetero-offsets. The L-like conduction band minima of silicon at the indirect band gap generally play no role.

An analogous picture would arise with p-doping in silicon. The corresponding transitions are clear to the expert.

The 1a to 1d thus show the inventive concept for the design of a semiconductor laser 10 or its structures. The inventive idea is to control the emission energy of a spatially indirect transition (type II transition) of two or three active sub-regions by means of doping. All known doping concepts can be used, in particular homogeneous doping, but also δ doping.

In addition to the band gap energies of the semiconductors used in the active structure, the band discontinuity at the interface (band offset) is of particular importance for the emission energy of the type II transition. Since the charge carriers recombine from the conduction band (LB or CB) of the other, the energy difference between the conduction band and the valence band is crucial for the emission. This discontinuity is determined in a first approximation by the exit energy and the Fermi level of the semiconductor heterostructure. If one does a semiconductor, this Fermi level shifts either in the direction of the conduction band LB (N-doping) or in the direction of the valence band VB (P-doping). Since the structures are spatially less extensive than the space charge zone, Fermi level pinning occurs. Thus, for example, for quantum films, quantum wires or quantum dots, the band discontinuity and thus the emission energy can be controlled and specifically manipulated by doping the semiconductor layers of the type II transition, i.e. by doping the sub-regions 30.

The concepts described here reflect a general property of semiconductors and semiconductor lasers. For this reason, the invention is not only limited to direct semiconductors, but is also transferable to indirect semiconductors, since only the gamma point is relevant. Furthermore, multinary compound semiconductors can also be realized in the active layer and the concept can be applied independently of the substrate platform, which is of great advantage, especially in industrial applications.

2 shows a possible modification of the basic concept, as represented for example by monolithic Grinsch (graded index of refraction separate confinement heterostructure). In contrast to the state of the art, these have a doped W structure, as explained above.

In addition to designing edge emitters, it is also possible to design surface emitters, such as 3 Here, the type II structure is monolithically applied and grown on a contacted n-type (or p-type) Bragg reflector and enclosed by a ring contact 50. A p-type (or n-type) Bragg reflector can then be deposited on the active layer. Such a structure represents a vertical-cavity surface-emitting laser (VCSEL). Alternatively, the structure can be closed with a cover layer to enable an external resonator configuration and to obtain a vertical external cavity surface-emitting laser (VECSEL). In contrast to the prior art, these have a doped W structure, as explained above.

Claims (10)

Semiconductor laser with semiconductor material systems made of elements for a semiconductor, comprising a substrate region (12), which is a substrate made of at least one carrier material, and at least one active region (20) with three sub-regions (30); a separation region (14), which is a barrier between the substrate region (12) and the active region (20), or between several repetitions of active regions (20), between sub-regions (30) of an active region (20) or between the active region (20) and the interface with the air; wherein the first active sub-region (32) is a doping region and has a semiconductor material system made of at least one element and a doping; the second active sub-region (34) is a doping region and has a doping and a further semiconductor material system made of at least one element that differs from the semiconductor material system of the first active sub-region (32); the third active sub-region (36) is a doping region and has the semiconductor material system of the first active sub-region (32); and the active region (20) of the semiconductor laser (10) has a doped W structure; and at least one of the semiconductor material systems in the second active sub-region (34) and/or in the first active and third active sub-regions (32, 36) is doped such that the band gap in the W structure can be adjusted in a predetermined manner such that the emission energy of the semiconductor laser (10) can be adjusted for emission energies smaller than the transition energies of the individual sub-regions (30); and at least one element of the semiconductor material system of the second active sub-region (34) comprises at least one element semiconductor and a doping. semiconductor lasers according to claim 1 , characterized in that the second active sub-region (34) has a different doping than the first active sub-region (32) and the third active sub-region (36). semiconductor lasers according to claim 1 , characterized in that the at least one element of the semiconductor material system of the second active sub-region (34) comprises at least one element semiconductor from the fourth main group. Semiconductor laser according to one of the preceding claims, characterized in that at least one element of the semiconductor material system of the first and third active sub-regions (32, 36) comprises an alloy of metal, preferably of metal of the third or fifth main group, particularly preferably with different dopings. Semiconductor laser according to the preceding claim, characterized in that the semiconductor material system of the first and third active sub-regions (32, 36) comprises alloys of metal, preferably of metals of the third and the fifth main group, particularly preferably with different doping levels. Semiconductor laser according to one of the preceding claims, characterized in that at least one of the active sub-regions (30) comprises a semiconductor material system made of at least one metal and one gas, wherein preferably the other active sub-region(s) (30) are alloy semiconductors made of at least one semiconductor material. Semiconductor laser according to one of the preceding claims, characterized in that the first active sub-region (32) and the third active sub-region (36) comprise a semiconductor material system with two different elements made of semiconductor materials. Semiconductor laser according to one of the preceding claims, characterized in that the first active sub-region (32) and the third active sub-region (36) each have a greater width than the second active sub-region (34), wherein preferably the width of the first active sub-region (32) and the third active sub-region (36) are at least 1.5 times as large as the width of the second active sub-region (34). Semiconductor laser according to one of the preceding claims, characterized in that the semiconductor material system in the second active sub-region (34) is an indirect semiconductor and the semiconductor material system in the first and third active sub-regions (32, 36) is a direct semiconductor. Semiconductor laser according to one of the preceding claims, characterized in that the semiconductor material system in the second active sub-region (34) is a direct semiconductor and the semiconductor material system in the first and third active sub-regions (32, 36) is an indirect semiconductor.

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