JP2002111042A - Infrared detection method - Google Patents

Abstract

(57) [Summary] [Problem] A conventional quantum well infrared detector has a detection capability (De
tectivity) was insufficient. SOLUTION: The present invention is an infrared detection method for irradiating light (inter-band light) 30 corresponding to inter-band energy, thereby increasing the number of carriers involved in detection of infrared 20 and improving the detection capability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detection method using an infrared detector having a multiple quantum well structure using a compound semiconductor.

[0002]

2. Description of the Related Art High-precision semiconductor quantum well structures can be manufactured by techniques such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOVPE). By applying this technology, quantum well infrared detectors (Quantu
m Well Infrared Photodetector = QWIP) is provided. In the QWIP, the height of the energy barrier of the quantum well and the thickness of the well layer can be designed relatively arbitrarily, and therefore, it is possible to flexibly cope with a wider wavelength than a detector using interband transition. There are advantages. Furthermore, it is also possible to manufacture detectors corresponding to a plurality of wavelength bands, for example, a 3-5 μm band and an 8-12 μm band. QWIP detectability (Detectivity) D is _{D = (η a P e /} 2πν) (τ L / nl) 1/2 (1) η a = (1-exp (-2αl)) / 2 (2) P e = 1 / (1 + τ _e / τ _r ) (3) Here, ν is the frequency of infrared light, τ _L is the lifetime of the hot carrier, n is the number of carriers, l is the thickness of the quantum well, α is the absorption coefficient, and τ _e is the escape time of the excited carrier from the well layer ( escape time), τ _r is the recapture time until the excited carriers return to the ground level
It is. The relaxation between sub-bands in a semiconductor quantum well is very fast, and the relaxation time, ie, the recapture time here, is generally on the order of picoseconds, especially on the order of 0.1 picoseconds for nitride semiconductors. This limits the detection capability of QWIP.

[0003]

As described above, the semiconductor quantum well infrared detector has the characteristics of flexibility with respect to wavelength and adaptability to multiple wavelengths. However, the intersubband relaxation process is extremely fast. Therefore, there is still room for improvement in terms of detection ability.

The present invention has been made in view of the conventional problems, and provides a novel infrared detecting method using a semiconductor quantum well infrared detector.

[0005]

In order to solve the above-mentioned problems, the present invention improves the detectivity by irradiating a semiconductor quantum well infrared detector with light having a wavelength corresponding to the inter-band transition energy. It is a way to make it. This will be described in detail below.

FIG. 1 schematically shows an energy band diagram of QWIP. Electrons 101 are supplied from one electrode 100 of the QWIP, and are supplied to the ground level 102 of each quantum well.
Move by tunnel effect. At this time, when infrared rays that resonate with the energy difference between the first ground level and the continuous level 103 on the well enter, the electrons are excited and flow to the other electrode 104 by the electric field applied to the quantum well. At this time, if light (inter-band light) having a wavelength corresponding to energy equal to or more than the energy difference between the electron ground level and the hole ground level 105 is formed, an electron-hole pair is formed. This will increase the number of electrons that contribute to infrared absorption.

Now, it is assumed that the number of electrons has been doubled by the inter-band light. As a result, the denominator of the expression (1) representing the detection capability described above increases by √2 times, and the absorption coefficient increases by 2 times. In the case of a normal quantum well structure, α is on the order of 1000 cm ⁻¹ and l is on the order of 100 nm.
Is much smaller than 1. At this time, the value of equation (2) can be approximated to αl. Therefore, if the absorption coefficient increases twice, the value of equation (2) also increases almost twice. As a result, (1)
The value of the equation increases by about $ 2. In this way, the detection ability can be increased by irradiating the light between the bands. Note that, by irradiating the interband light, an electron-hole pair is also generated in the contact layer, and this becomes a photocurrent. This can be avoided by setting the band gap of the contact layer larger than the energy of the inter-band light. This also serves as a barrier to holes, and can also suppress a current component due to holes generated in the quantum well.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram schematically showing an infrared detecting method according to the first embodiment of the present invention. A light source 31 that emits the interband light 30 is provided at a position facing the quantum well infrared detector 1 and not interfering with the incidence of the infrared light 20. FIG. 3 schematically shows the infrared detector 1 in the present embodiment. About thickness in FIG. 3 1.8 nm of Al _{0. 5} G
a _0.5 N barrier layer 2 a and a GaN well layer 2 b having a thickness of about 20 nm
Multiple quantum well structure 2 composed by repeating the period
_Are laminated on the sapphire substrate 5 so as to be sandwiched between the n ^- Al _0.25 Ga _0.75 N contact layers 3 and 4.
The multiple quantum well structure has a detection sensitivity to infrared rays having a wavelength of 2 μm. Such a laminated structure can be manufactured by using, for example, the MOVPE method.
Next, a part of the contact layer 4 is exposed by etching, and gold is vapor-deposited to form an electrode 6. Further, gold is vapor-deposited on the contact layer 3 to form a grating 7.
This detector is cooled using liquid nitrogen. As the inter-band light 30, ultraviolet light having a wavelength of 310 nm or less cut by a filter is used. At this wavelength, no electron-hole pairs are generated in the contact layer because the band gap of the contact layer corresponds to a wavelength of about 300 nm.

FIG. 4 is a view for explaining a second embodiment according to the present invention. In the figure, a reflecting mirror 40 is provided at a position that does not hinder the incidence of the infrared ray 20, and the interband light 30 emitted from the light source 31 is reflected by the reflecting mirror 40 and applied to the detector 1.

FIG. 5 is a view for explaining a third embodiment according to the present invention. In the figure, the infrared ray 20 of the detector is shown.
The reflection mirror 50 is installed on the incident path of. This reflector is formed so that a dielectric multilayer film is formed and has a high reflectance for the inter-band light 31 but a high transmittance for the infrared light. Have been. Thereby, the incident infrared light 20 passes through the reflecting mirror 50 and reaches the detector 1, while the inter-band light 30 is reflected by the reflecting mirror 50 and reaches the detector 1.

Further, in the above-described embodiment, the detector 1 is made of a nitride semiconductor. However, the present invention is not applied only to a nitride semiconductor, but may be made of another material, for example, a nitride semiconductor.
It is also applicable to AlGaAs / GaAs quantum well detectors. In this case, it is needless to say that the inter-band light is not necessarily ultraviolet light but corresponds to each material.

[0013]

As described above, according to the present invention, the detection capability of the quantum well infrared detector (QWIP) can be improved.
ity) can be improved.

[Brief description of the drawings]

FIG. 1 is an energy band diagram of a quantum well infrared detector.

FIG. 2 is a schematic view showing a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of an infrared detector according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a third embodiment of the present invention.

[Explanation of symbols]

1: Quantum well infrared detector 20: Infrared ray 30: Interband light 31: Light source 2: Multiple quantum well structure 2a: Al _0.5 Ga _0.5 N barrier layer 2b: GaN well layer 3, 4: Contact layer 5: Sapphire substrate 6 : Electrode 7: Grating

Claims (4)

[Claims] 1. A barrier layer and a well layer comprising a compound semiconductor are repeatedly laminated to form a multiple quantum well structure, and a transition between energy levels of electrons or holes formed in the well layer is utilized. Detecting an infrared ray by irradiating light having a wavelength corresponding to an energy difference between the ground level of electrons and the ground level of holes. 2. The infrared detecting method according to claim 1, wherein said compound semiconductor is composed of a nitride semiconductor. 3. The infrared detecting method according to claim 1, wherein the repetition of the barrier layer and the well layer is periodic. 4. A contact layer having n-type conductivity is provided at both ends of the multiple quantum well layer, and a band gap of the contact layer is larger than an energy corresponding to the wavelength of light applied to the contact layer. Claim 1 characterized by the following:
Infrared detection method as described.