PtSi Schottky-barrier focal plane arrays for multispectral imagingin ultraviolet, visible, and infrared spectral bands

PtSi Schottky-barrier detectors, which are conventionally used in the back-illumination mode for thermal imaging in the 3-5-μm infrared (IR) spectral band, are shown to exhibit excellent photoresponse in the near-ultraviolet and visible regions when operated in the front-illumination mode. For devices without antireflection coatings, external quantum efficiency in excess of 60% has been obtained for wavelengths between 400 and 800 nm. The efficiency decreases below 400 nm but is still about 35% at 290 nm. High-quality imaging has been demonstrated in both the visible and 3-5-μm spectral bands for front-illuminated 160×244-element PtSi focal plane arrays integrated with monolithic CCD readout circuitry     

High responsivity GaInAs PIN photodiode by using erbium gettering

In this article, we grow the GaInAs layers by introducing the rare-earth element Er into the GaInAs solutions for liquid-phase epitaxy without any complicated processes or an extended bakeout of the growth melts. The dominant process occurring during the growth of GaInAs layers in the presence of Er is a very efficient gettering of residual donors. By using an Er-doped GaInAs layer as the intrinsic layer in the PIN structure, the room temperature front-illuminated PIN photodiodes exhibit good quantum efficiencies of 60% at 1.3 μm and 83% at 1.6 μm for devices with antireflection coatings, which are better than those of 52% at 1.3 μm and 65% at 1.6 μm for the front-illuminated devices without Er doping and comparable to those of 63% at 1.3 μm and 74% at 1.6 μm for commercially available back-illuminated photodiodes. These devices also have a rise time of 88 ps and a pulsewidth of 162 ps for response speed and useful sensitivity to about 3.6 GHz. The detectors respond to pseudo-random modulation at bit rates up to 2.5 Gb/s with a clear eye opening and error free     

A wide spectral band photodetector with PtSi/p-Si Schottky-barrier

The photoresponse of a front-illuminated PtSi Schottky-barrier detector is measured in the wavelength range between 0.4 and 5.2μm. In the wavelength range longer than 1.1μm, the detection mechanism is the internal photoemission. On the other hand, the intrinsic mechanism becomes dominant in the wavelength range shorter than 1.1μm. The measured data are in good agreement with values calculated from these two detection mechanisms. The photoresponse depends on the PtSi thickness in both wavelength ranges. For getting a high responsivity, it is important to make a thin uniform metal film. The visible and the thermal image with a PtSi Schottky-barrier wide spectral band imager are also demonstrated.     

Pt_xIr_(1-x)Si/p-Si红外探测器的研制

使用超高真空磁控溅射系统在p-Si上制备了铂铱硅(Pt_xIr_(1-x)Si)薄膜,并制作了Pt_xIr_(1-x)Si/p-Si红外探测器,研究了探测器在3～5 μm波段的特性,结果表明,Pt_xIr_(1-x)Si/p-Si势垒高度为0.177 eV,相应红外探测器截止波长为7.0μm.与普通铂硅红外探测器相比,铂铱硅红外探测器在3～5μm中波红外波段响应明显增强.

Abstract：

Ultra thin Pt_xIr_(1-x)Si films were deposited on p-Si substrates with ultra high vacuum sputtering system and Pt_xIr_(1-x)Si /p-Si(100) Schottky barrier detectors were fabricated and the characteristics of the detectors operating in the wavelength range of 3 ～ 5 μm were studied, with the barrier height of 177 meV and cutoff wavelength of 7. 0 μm. compared with ordinary Pt-Si IR detectors, Pt_xIr_(1-x)Si detectors have a much higher response at 3～5 μm MWIR spectral range.     

IrSi Schottky-barrier infrared detectors with 10-μm cutoffwavelength

IrSi Schottky-barrier detectors were fabricated with ~40-Å-thick silicide electrodes formed on p-type Si substrates by in situ processing in a conventional electron-beam evaporator. High-resolution transmission electron microscopy shows that these detectors have clean, abrupt silicide-Si interfaces. For operation at a reverse-bias voltage of 2 V, the cutoff wavelength is ~10 μm, as determined by quantum efficiency measurements     

Photoresponse model for Si1-xGex/Siheterojunction internal photoemission infrared detector

A photoresponse model has been developed for the Si_1-xGe_x/Si heterojunction internal photoemission (HIP) infrared detector at wavelengths corresponding to photon energies less than the Fermi energy. A Si_0.7Ge_0.3/Si HIP detector with a cutoff wavelength of 23 μm and an emission coefficient of 0.4 eV^-1 has been demonstrated. The model agrees with the measured detector response at λ>8 μm. The potential barrier determined by the model is in close agreement (difference ~4 meV) with the potential barrier determined by the Richardson plot, compared to the discrepancies of 20-50 meV usually observed for PtSi Schottky detectors     

Silicide/strained Si1-xGex Schottky-barrierinfrared detectors

By employing a thin silicon sacrificial cap layer for silicide formation, the authors successfully demonstrated Pd₂Si/strained Si_1-xGe_x Schottky-barrier infrared detectors with extended cutoff wavelengths. The sacrificial silicon eliminates the segregation effects and Fermi level pinning which occur if the metal reacts directly with Si_1-x Ge_x alloy. The Schottky barrier height of the silicide/strained Si_1-xGe_x detector decreases with increasing Ge fraction, allowing for tuning of the detector's cutoff wavelength. The cutoff wavelength was extended beyond 8 μm in PtSi/Si _0.85Ge_0.15 detectors. It is shown that high quantum efficiency and near-ideal dark current can be obtained from these detectors     

Edge leakage control in platinum-silicide Schottky-barrier diodesused for infrared detection

Platinum silicide (PtSi) on p-silicon Schottky-barrier focal plane arrays (FPAs) are strong candidates for infrared (IR) detection up to a wavelength of about 5 μm. However, an inherently low quantum efficiency (about 1% at 4 μm) makes it important to maximize the fill factor or the area of the array that is IR-sensitive. Current designs use an n^- guard ring around the PtSi diodes to suppress edge leakage. This is effective, but the guard-ring overlap can significantly reduce the sensitive area of the diode. An aluminium plate that is already used as a photon reflector above the diode in current designs can be positively biased as a field plate to create a surface depletion layer around the diode periphery. This produces leakage current suppression equivalent to the guard ring without giving up IR-sensitive diode area     

HgCdTe Quantum Detection: from Long-Wave IR down to UV

A few years ago, visible detection was demonstrated using advanced substrate thinning processes on flip-chip hybridized HgCdTe focal-plane arrays, in both French and US laboratories. Constant quantum efficiency was demonstrated at LETI-Sofradir from the short-wave infrared (IR) (2.5 μm cut-off) down to the visible range in 2006, validating complete CdZnTe substrate removal. This paper presents and discusses HgCdTe photodiode spectral response characterization, focusing on the short-wavelength part of the spectrum. We confirm the extended sensitivity of middle- and long-wave diodes: constant quantum efficiency has been observed from 10 μm down to 230 nm in the ultraviolet (UV). Such a unique property may be useful for very large-bandwidth spectrometers requiring monolithic detectors. Avalanche gain of middle-wave avalanche photodiodes has also been investigated in both the visible and the UV range. We demonstrate here that the avalanche gain remains constant while keeping a very low excess noise factor. This result opens the way to low-flux applications in this wavelength range.     

Two-colour quantum well infra-red photodetector with peaksensitivities at 3.9 and 8.1 μm

A two-colour infra-red photodetector using multistacks of GaAs/AlGaAs quantum wells is demonstrated. The response peaks are at 3.9 and 8.1 μm. The peak responsivities of the detector are 0.4 A/W and 35 A/W for 8.1 μm and 3.9 μm bands, respectively. The detectivities of the 3.9 and 8.1 μm bands are 7.5×10⁹ and 1.5×10¹⁰ cmHz^1/2/W. These values are the best reported results for two-colour detectors with peak sensitivities in the spectral regions of 3-5 and 8-12 μm     

AlGaN/GaN HEMTs on silicon substrates with fT of 32/20GHz and fmax of 27/22 GHz for 0.5/0.7 μm gate length

AlGaN/GaN HEMTs on silicon substrates have been realised and their static and small signal characteristics investigated. The AlGaN/GaN (x=0.23) material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current density of 0.53 to 0.68 A/mm and a peak extrinsic transconductance of 110 mS/mm. A unity gain frequency of 20 and 32 GHz and a maximum frequency of oscillation of 22 and 27 GHz are obtained for devices with a gate length of 0.7 and 0.5 μm, respectively. These values are the highest reported so far on AlGaN/GaN/Si HEMTs and are comparable to those known for devices using sapphire and SiC substrates     

IrSi Schottky-barrier infrared detectors with wavelength responsebeyond 12 μm

Schottky-barrier infrared detectors with a 4-nm-thick IrSi electrode have been fabricated on p-Si substrates previously implanted with low-energy boron ions. Low-energy boron ion implantation has been used to form a shallow p⁺-Si layer that lowers the barrier height of IrSi-Si Schottky-barrier contacts by the image-force effect and field-assisted tunneling. IrSi infrared detectors with a cutoff wavelength beyond 12 μm have been obtained by this technique. The optical barrier height found by spectral response measurements is 0.100 eV, which corresponds to a detector cutoff wavelength of 12.4 μm     

Optical devices from AlGaAs-GaAs HBTs heavily doped with amphotericSi

A new optoelectronic multifunctional device, having triple function of light emission, detection and amplification have been developed and some preliminary integrated circuits are demonstrated. The devices consist of N-p-n or N-P-n AlGaAs-GaAs HBT utilizing amphoteric Si heavily-doped GaAs or AlGaAs p-type base layer. Maximum current gain of 3600, and light output power of about 0.17 μW with 100 μA base current (I_b) in transistor mode operation and of about 10 μW with I_b=40 mA in diode mode operation are obtained. The optical emission wavelengths in both are about 0.85-0.86 μm. Optical gain of about 130 was obtained near the 0.86 μm wavelength as a detection transistor. Spectrum matching between emission and detection wavelength range is achieved. Some monolithic integrated circuits constituted of the transistors are proposed and demonstrated successfully. The relationship between current gain and radiative quantum efficiency at the transistor operation is also discussed     

7-μm-cutoff PtSi infrared detector for high sensitivity MWIRapplications

PtSi Schottky infrared detectors with extended cutoff wavelengths of 5.7, 6.6, and 7.3 μm have been demonstrated by incorporating a thin p+ layer at the PtSi-Si interface for high sensitivity medium wavelength infrared imaging applications. The response uniformity of the 7-μm cutoff detector was studied     

Single-electron effect in PtSi/porous Si Schottky junctions

PtSi/porous Si schottky junctions exhibit a breakdown type current-voltage (I-V) curve in reverse bias mode. Below breakdown their current density is much less than regular PtSi/Si junctions. The breakdown voltage decreases with application of infrared radiation for both n and p-type junctions. N-type junctions are sensitive to IR wavelengths of up to 7 /spl mu/m even at room temperature. The small reverse bias current, the change of breakdown voltage with radiation, and IR sensitivity at room temperature can all be explained by single-electron effect. Numerical results show that representative porous schottky junctions exhibit depletion capacitances in 10/sup -19/ f range which is enough to observe single-electron effect at room temperature. Single-electron effect and avalanche multiplication can explain existing experimental data.     

（英）磁控溅射制备纳米晶GZO/CdS双层膜及GZO/CdS/p-Si异质结光伏器件的研究

本文中,采用磁控溅射制备Ga掺杂ZnO (GZO)/CdS双层膜在p型晶硅衬底上以形成GZO/CdS/p-Si异质结器件。纳米晶GZO/CdS双层膜的微结构、光学及电学特性,通过XRD、SEM、XPS、紫外-可见光分光光度计和霍尔效应测试系统表征。GZO/CdS/p-Si异质结J-V曲线显示良好的整流特性。在±3V时,整流比IF/IR(IF和IR分别表示正向和反向电流)已达到21。结果表明纳米晶GZO/CdS/p-Si异质结具有好的二极管特性,在反向偏压下获得高光电流密度。纳米晶GZO/CdS/p-Si异质结显示明显的光伏特性。由于CdS晶格常数在GZO和晶Si之间,它能作为一个介于GZO和晶Si之间的缓冲层,能有效地减少GZO和p-Si之间的界面态。因此,我们获得了GZO/CdS/p-Si异质结明显光伏特性。     

A silicon homojunction infrared detector having an active metalfilm on an n++ layer

A silicon n⁺⁺pn homojunction infrared detector, in which a degenerate n⁺⁺ layer is backed by a metal film forming an ohmic contact, has been proposed and studied. The metal film is a photoelectric conversion region along with the n⁺⁺ layer. Although, for an n⁺⁺pn detector without the metal film, very poor rectifying properties are observed when the n⁺⁺ layer thickness is extremely reduced, the new detector, employing a thin PtSi film as the metal film, shows normal diode I-V characteristics, since the PtSi film provides increased surface conductivity. The new detector has achieved an increase in operatable temperature, or an extension of cutoff wavelength, and operated with cutoff wavelengths of 11.9 μm, 18.7 μm and about 30 μm at 70 K, 50 K, and 30 K, respectively, because the saturation current density for the new detector has been reduced to about one tenth that for the previously reported n⁺⁺pn detector. The responsivity for the new detector has increased to 1.1-3.8 times as large as that for the previously reported n⁺⁺pn detector, when both detectors have the same cutoff wavelength     

Potential of asymmetrical Si/Ge and Ge/Si based hetero-junction transit time devices over homo-junction counterparts for generation of high power

Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction Double-Drift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique,developed by the authors,for operation in the Ka-,V- and W-band frequencies.The results are further compared with corresponding Si and Ge homo-junction devices.The study shows high values of device efficiency,such as 23%, 22%and 21.5%,for n-Ge/p-Si IMPATTs at the Ka,V and W bands,respectively.The peak device negative conductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7×10~6 S/m~2 and 71.3×10~6 S/m~2, which are～3-4 times better than their Si and Ge counterparts at the V-band.The computed values of RF power-density for n-Ge/p-Si hetero-junction IMPATTs are 1.0×10~9,1.1×10~9 and 1.4×10~9 W/m~2,respectively,for Ka-,V- and W-band operation,which can be observed to be the highest when compared with Si,Ge and n-Si/p-Ge devices.Both of the hetero-junctions,especially the n-Ge/p-Si hetero-junction diode,can thus become a superior RF-power generator over a wide range of frequencies.The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.     

Long-wavelength GexSi1-x/Si heterojunctioninfrared detectors and 400×400-element imager arrays

Heterojunction Ge_xSi_1-x/Si internal photoemission infrared detectors exhibiting nearly ideal thermionic-emission dark-current characteristics have been fabricated with cutoff wavelengths out to 16 μm. High-quality imaging without uniformity correction has been demonstrated in the long-wavelength infrared (LWIR) spectral band for 400×400-element focal plane arrays consisting of Ge_0.44Si_0.56 detectors with a cutoff wavelength of 9.3 μm and monolithic charged-coupled-device readout circuitry. The Ge_0.44Si_0.56 composition was chosen in order to obtain a barrier height low enough to yield a cutoff length within the LWIR band, but high enough to permit low dark-current operation at about 50 K     

Comparison of GaN and 6H-SiC p-i-n photodetectors with excellentultraviolet sensitivity and selectivity

We fabricated GaN and 6H-SiC p-i-n photodetectors and compared their electrical and optical characteristics. The GaN diodes suffered from significant leakage current of 37 μA/mm² at -5 V, while the SiC diode leakage current was below the noise level at 10 pA/mm² at -20 V. The built-in potentials and the unintentional “i-layer” doping densities were obtained from capacitance-voltage (C-V) measurements. The SiC detectors exhibited a broad spectral response in contrast to the abrupt cutoff observed in the GaN detectors. The peak responsivities of the GaN and SiC photodetectors corresponded to internal quantum efficiencies of 57% at 3.42 eV and 82% at 4.49 eV, respectively. Furthermore, both detectors exhibited excellent visible rejection ratios which is needed for solar-blind applications. The response times at zero bias were 18 and 102 ns for the GaN and SiC detectors, respectively