Porous Silicon Photodetectors
Fabrication of Porous Silicon Based Photodetectors for Visible and UV Ranges and Study of their Properties
Tech Area / Field
- INS-DET/Detection Devices/Instrumentation
8 Project completed
Senior Project Manager
Bunyatov K S
State Institute of Rare Metals, Russia, Moscow
- Tbilisi State University, Georgia, Tbilisi\nNPO Orion, Russia, Moscow
- University of Rochester, USA, NY, Rochester\nDe Montfort University, UK, Leicester
Project summaryThe main purposes of this project are fabrication and investigation of porous silicon (PS) - based photodetectors. As a result, a laboratory technology will be developed and samples of PS -based photodetectors for visible and near UV ranges will be fabricated. It is expected that these detectors will have better parameters as compared to monocrystalline silicon (c-Si) and A3B5 based photodetectors (response time of 2 ns and photosensitivity as large as 5 - 10 A/W in 0.4 - 0.7 mm range of spectrum could be obtained). Detectivity will be not worse than (1-4) ґ 1012 cm ґ Hz1/2w-1. An industrial technology of fabrication of PS-based photodetectors might be developed later in Moscow (Russia) and Tbilisi (Republic of Georgia) on the base of laboratory technology worked out during this project.
Fast-response photodetectors have numerous applications. They are used for example for optical communication systems, for astronavigation, for infrared sensitive devices, for ecological control of atmosphere. Participants of this project have large experience in designing of photodetectors for military purposes. Recently they investigated optical, structural and photoelectric properties of new semiconductor material - porous silicon and began investigation of PS-based photosensitive structures [1 - 4].
It is known that the photosensitivity of PS-based device structures is determined by the potential barrier that exists is c-Si substrate on the PS/c-Si heterojunction [4, 5]. Therefore, PS-based device structure operates as heterojunction photodiode. Porous silicon has large bandgap (1.4 – 2.2 eV depending on the porosity) and serves as optical window, passing the light to c-Si substrate. This leads to increase of ultraviolet photosensitivity and decrease of the response time. Earlier, metal/PS/c-Si (p-type) and metal/p-PS/n-PS/c-Si photodiode structures were fabricated  that have photosensitivity spectrum typical for c-Si based photodiodes. Due to antireflecting properties of PS layer (refraction coefficient of PS is equal to 1.45 – 2.5) photosensitivity of these structures is close to theoretical limit for unity quantum efficiency photodiode (0.7 A/w at 0. 9 mm and 0.5 A/w at 0. 63 mm). Metal/p-PS/n-PS/c-Si structures have detectivity of about 5 ґ 1011 cm ґ Hz1/2w-1 which value is close to that for c-Si p-i-n photodiodes and the response time of 2 ns (about 10 times less than that for c-Si p-i-n photodiodes). Metal/PS/c-Si structures have 100 times larger dark reverse current and, hence, less detectivity.
Authors of this project also obtained metal/PS/c-Si (p-type) structures with photosensitivity values and spectrum typical for PS based structures in Ref. . But detectivity of our metal/PS/c-Si structures was close to that for metal/n-PS/p-PS/c-Si structures in Ref. . Preliminary experiments have indicated that dark reverse current could be farther decreased (more than 10 times) and the detectivity could be increased by using electrochemical doping of PS by In. Besides that, metal/PS/c-Si structures were fabricates that have photosensitivity values of about 10 A/W, which value is higher than that for unity quantum efficiency photodiode, but these structures have less detectivity.
Under this project it is supposed to optimize the technology and the design of metal/PS/c-Si structures and fabricate photodetectors with better device parameters. Authors also plan to fabricate metal/n-PS/p- PS/c-Si and metal/p-PS/n-PS/c-Si photodiode structures, which will lead to decrease of dark reverse currents and increase of the detectivity. Preparation technology of n-type PS layer is more complicated because the illumination is used under etching process and physical properties of PS layer depend on the illumination intensity and spectrum. Transport properties of these structures and doping of PS by In and other impurities (p, b) will be studied.
Prime cost of the PS based photodetector will be about 30 U. S. dollars while its price is 50 U. S. dollars. Under production of two thousands photodetectors per year project expenses will be compensated after two years. Other organizations are invited for collaboration.
1. L. A. Balagurov et al., J. Appl. Phys. 79, 4811 (1996).
2. L. A. Balagurov et al., J. Appl. Phys. 80, 574 (1996).
3. К A. Balagurov et al., Appl. Phys. Lett. 69, 2582 (1996).
4. L. A. Balagurov et al., J. Appl. Phys. (to be published).
5. J. P. Cheng et al., Appl. Phys. Lett. 61, 459 (1992).