Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Patent
1997-11-07
2000-08-29
Tran, Minh Loan
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
257 19, 257 21, 257 22, 257432, 257436, H01L 2906, H01L 310232
Patent
active
061112666
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The current invention relates to a method of realising reflectors of electromagnetic radiation in semiconductor substrates upon which high quality epitaxy can be grown. These substrates may be used to produce a resonant cavity for electromagnetic radiation: such cavities are of importance for applications such as laser etalons and infrared photon detectors.
2. Discussion of Prior Art
Infrared detectors are of importance for both civilian and military applications. Where radiation is transmitted through the atmosphere the useful wavelength ranges are limited to [3-5].times.10.sup.-6 m and [7.5-14].times.10.sup.-6 m by atmospheric absorption. For military applications the long wavelength range may be further limited to about [7.5-9].times.10.sup.-6 m by filters designed to avoid dazzle by CO.sub.2 lasers. Focal plane arrays (FPAs) with many individual detector elements are used for imaging in both these ranges. Several technologies are available for FPAs in the [3-5].times.10.sup.-6 m range eg CdHgTe (CMT) or InSb hybridised to Si readout circuits, or monolithic arrays. The technology is less well developed in the [7.5-14].times.10.sup.-6 m range. CMT is difficult to grow with the uniformity required for long wavelength infrared (LWIR) FPAs and requires cold bonding to the Si readout circuit which makes fabrication more difficult. Multi Quantum Well (MQW) detectors using GaAs/AlGaAs have progressed to 128.times.128 arrays using solder bump technology to hybridise to a Si readout chip but with unknown yield for larger arrays (B. F. Levine. J. Applied Physics 74 R1 (1993)). High performance FPAS are typically operated at temperatures close to that of liquid nitrogen. The thermal mismatch between detector and readout chips limits the size of hybrid arrays using compound semiconductor detectors on Si readout circuits. There is no successful Si monolithic LWIR FPA technology; IrSi, which has a long wavelength infrared response has low quantum efficiency and therefore very low operating temperature.
At present LWIR technologies are being developed which are compatible with the Si readout circuits to avoid limitations inherent in the hybrid approach using compound semiconductor detectors. Of these the use of pseudomorphic heterostructures formed from silicon-germanium alloys epitaxially grown on Si substrates (SiGe/Si) is the most promising. Pseudomorphic SiGe/Si has the advantage of allowing a very high degree of uniformity over the Si substrate wafer which minimises fixed pattern noise in the FPA and favours high manufacturing yield.
LWIR photon detectors made from SiGe/Si MQWs are limited by low responsivity and by dark current thermal noise. Devices must be operated at lower temperatures to give acceptable signal
oise ratios. This restricts the utility and increases the cost of the imaging system. An increase in the quantum efficiency for absorption of incident radiation should improve the signal
oise ratio and so allow operation at higher temperature.
The quantum efficiency of detectors at shorter wavelengths (<2.times.10.sup.-6 m) has been enhanced using resonant cavities (see eg R Kuchibhotla, J Campbell. J C Bean, L Peticolas and R Hull, Appl. Phys. Lett 62 2215 (1993)). Resonant cavities produce localised regions of high electric field. Where absorption is dependent on the electric field the quantum efficiency can be enhanced by locating the absorbing region of a device in a resonant cavity.
To produce such a resonant cavity, the incident radiation wavelength .lambda., is confined between two reflectors. Electric field enhancement in the cavity increases as the reflectances of the confining mirrors at wavelength .lambda. increase. For a cavity of width L.sub.c and refractive index n, light confined in the cavity resonates at wavelengths determined by optical thickness nL.sub.c /.lambda., and the phase changes at the confining mirrors. Hence the cavity width, as well as the wavelength-dependence of the reflectors, must be chosen carefully to match
REFERENCES:
B.F. Levine, "Quantum-well infrared photodetectors", J. Appl. Physics 74 (8), Oct. 15, 1993.
R. Kuchibhotla et al, "GE.sub.0.2 Si.sub.0.8 /Bragg-reflector mirrors for optoelectronic device applications", Appl. Phys, Lett. 62 (18), May 3, 1993.
V.P. Kesan et al, "Si/SiGe heterostructures grown on SOI substrates by MBE for integrated optoelectronics", Journal of Crystal Growth, 111 (May 1991).
D.K. Nayak et al, "Photoluminescence of Si/SiGe/Si quantum wells on separation by oxygen implantation substrate" Appl. Phys. Lett. 64 (18), May 2, 1994.
Applied Physics Letters, Dec. 12, 1994, USA, vol. 65, No. 24, ISSN 0003-6951, pp. 3039-3041, XP000485921 Fukatsus et al: "Special modulation of luminescence of strained Si/sub 1-x/Ge/sub s//Si quantum wells in a vertical cavity with air/Si and Si/Sio/sub 2/interface mirrors" cited in the applicaton see the whole document.
Journal of Crystal Growth, vol. 111, No. 1/4, May 2, 1991, pp. 936-942, XP000298474 Kesan V P et al: Si/SiGe Heterostructures Grown on SOI Substrates by MBE for Integrated Optoelectronics: cited in the application see the whole document.
Photodetectors: Materials and Devices, San Jose, CA, USA, Feb. 1-2, 1996, vol. 2685, ISSN 0277-786X, Proceedings of the SPIE--The International Society for Optical Engineering, 1996, SPIE-Int. Soc. Opt. Eng, USA, pp. 188-194, XP000602727 Robbins D J et al: "Silicon-based resonant cavity detectors for long-wave infrared imaging" see the whole document.
Applied Physics Letters, Jan. 22, 1996, AIP, USA, vol. 68, No. 4, ISSN 0003-6951, pp. 544-546, XP000556076 Carline R T et al: "Long-wavelength SiGe/Si resonant cavity infrared detector using a bonded silicon-on-oxide reflector" see the whole document.
Carline Roger T
Robbins David J
The Secretary of State for Defence in Her Britannic Majesty's Go
Tran Minh Loan
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