MESFET fabrication on MOCVD grown Hg/sub 1-x/Cd/sub x/Te

The fabrication of the first MESFET structures on Hg/sub 1-x/Cd/sub x/Te is reported using MOCVD grown layers on GaAs substrates. The 6 mu m gate devices exhibited a room temperature transconductance of 1.0 mS/mm and pinch off voltage of -4.0 V. The Schottky barrier characteristics of the devices were critically dependent on the stoichiometric x ratio of the Hg/sub 1-x/Cd/sub x/Te with diode formation evident only at x >0.5.<>     

Hg_（1－x）Cd_xTe液相外延薄膜的光致发光

用红外光荧光测量分析了Ｈｇ１－ｘＣｄｘＴｅ液相外延薄膜的发光特性，观察到局域激子及束缚激子发光．当外延层减薄至２μｍ后，ＰＬ信号的峰位将向高能方向移动，这是由于外延薄膜纵向组份不均匀引起的     

1-2 micron (Hg, Cd)Te photodetectors

The performance of mercury cadmium telluride detectors in the 1-2 micron spectral region has been predicted from basic material parameters. Photovoltaic devices should be characterized by specific responsivities of 1 A/W for a 1000 ohm load when transit time limited to less than 20 ns. Photoconductive detectors made from n-type material should have radiative lifetimes of 1 ms. The feasibility of high performance 1-2 micron (Hg, Cd)Te detectors has been demonstrated experimentally. Deep junction devices operating at room temperature without bias have been fabricated by impurity indiffusion. Detectivities at 1.75 microns approached 10¹⁰cm.Hz^1/2/W with open-circuit responsivities of approximately 500 V/W. In addition, 1.5 micron detectors have been fabricated from p-type, 25 Ω.cm material. With no bias at room temperature, these detectors showed D* λ>10¹⁰cm.Hz/12/W, open-circuit responsivities in excess of 10³V/W, and response times on the order of microseconds. These preliminary results indicate that detectors fabricated from the pseudobinary alloy of (Hg, Cd)Te are well suited for high speed, near infrared photodetection in which room temperature operation is required.     

Effects of growth conditions on the composition of CVT and PVT grown Hg1-x Cd x Te epitaxial layers

Single crystal epitaxial layers of Hg_1-x Cd _x Te were grown on CdTe substrates employing the chemical and physical vapor transport techniques. Different growth temperatures and various pressures of HgI₂ as a transport agent were used while the source materials had compositions of eitherx = 0.4 orx = 0.6. The epilayers are of nearly uniform composition to a depth of about one-half of the layer thickness. The Hgl₂ pressure and the growth temperature used for the growth experiments have significant effects on the layer composition. The desired epilayer composition ofx = 0.2 can be achieved with either source compositions by properly adjusting the HgI₂ pressure and the growth temperature.     

AlxZn1-xO合金MSM光电探测器的研究

在Si衬底上磁控溅射制备AlxZn1-xO(AZO)合金薄膜,在其上真空蒸发Ni/Au叉指电极获得金属-半导体-金属(MSM)结构光电探测器.采用UV-Vis-Nir分光光度计测量AZO系列薄膜的光吸收特性,观察到AZO 合金薄膜的光学吸收带边随Al含量增加明显蓝移.测试AZO探测器的电流电压特性、时间特性和响应光谱发...     

Hg_（1－x）Cd_xTe的扫描光致发光研究

用傅里叶变换红外扫描光致发光方法研究了Ｈｇ１－ｘＣｄｘＴｅ体单晶样品，该方法可直接得到ＨｇＣｄＴｅ晶片组分的二维平面分布，并可得到辐射复合在复合机制中所占比重的平面分布，以及晶体中非平衡载流子寿命的分布     

热处理过程中Hg1—xCdxTe／CdTe界面互扩散研究

对ＨｇＣｄＴｅ／ＣｄＴｅ／ＧａＡｓ结构热处理后的样品进行深度剥层腐蚀,并用椭偏光谱测量方法,获得了样品在４９０℃经０．５ｈ和２ｈ热处理后不同深度下的组份分布．根据实验结果对Ｚａｎｉｏ等人提出的扩散系数公式进行了修正,得到４９０℃热处理条件下的组份扩散系数ＤＨｇ１－ｘＣｄｘＴｅ（４９０℃）＝４×１０－３×１０－３·ｘ．     

Hg1—xCdxTe光导探测器的电学参量分析

测量了Ｈｇ１－ｘＣｄｘＴｅ光导探测器中电阻率与温度及磁场强度的关系．在Ｓｈｕｂｎｉｋｏｖ－ｄｅＨａａｓ（ＳｄＨ）测量中,发现了表面电子的浓度在１．２～５５Ｋ的范围内没有变化．一个包括体电子和两类表面电子的三带模型被用来分析电阻率随温度变化的关系,由此得到的电学参数与实验及ＳｄＨ测量获得的结果非常符合     

n-Hg_（1－x）Cd_xTe中复合中心

利用深能级瞬态谱（ＤＬＴＳ）研究了Ｈｇ１－ｘＣｄｘＴｅ（ｘ＝０．４）ｐ＋ｎ结中Ｈ２（０．２９）空穴陷阱的俘获机制，发现它不满足级联复合机制或俄歇复合机制，该能级俘获截面的温度关系满足σ（Ｔ）＝σ∞ｅｘｐ（－ＥＢ／ｋＴ）形式，推测多声子无辐射复合起着决定性作用     

Investigations of high-performance GaAs solar cells grown on Ge-Si/sub 1-x/Ge/sub x/-Si substrates

High-performance p/sup +//n GaAs solar cells were grown and processed on compositionally graded Ge-Si/sub 1-x/Ge/sub x/-Si (SiGe) substrates. Total area efficiencies of 18.1% under the AM1.5-G spectrum were measured for 0.0444 cm/sup 2/ solar cells. This high efficiency is attributed to the very high open-circuit voltages (980 mV (AM0) and 973 mV (AM1.5-G)) that were achieved by the reduction in threading dislocation density enabled by the SiGe buffers, and thus reduced carrier recombination losses. This is the highest independently confirmed efficiency and open-circuit voltage for a GaAs solar cell grown on a Si-based substrate to date. Larger area solar cells were also studied in order to examine the impact of device area on GaAs-on-SiGe solar cell performance; we found that an increase in device area from 0.36 to 4.0 cm/sup 2/ did not degrade the measured performance characteristics for cells processed on identical substrates. Moreover, the device performance uniformity for large area heteroepitaxial cells is consistent with that of homoepitaxial cells; thus, device growth and processing on SiGe substrates did not introduce added performance variations. These results demonstrate that using SiGe interlayers to produce "virtual" Ge substrates may provide a robust method for scaleable integration of high performance III-V photovoltaics devices with large area Si wafers.     

1/f Noise in (Hg, Cd)Te photodiodes

In this article we present results of experiments to characterize 1/fnoise in Hg0.7Cd0.3Te n⁺-on-p junction photodiodes. Under zero-bias voltage conditions, the photodiodes display no 1/fnoise, even in the presence of large photocurrents. Under reverse-bias voltage operation, 1/fnoise is observed. In these experiments, the 1/fnoise was measured as a function of temperature, diode bias voltage, and photon flux. Since these parameters varied the relative contributions of the various current mechanisms, the diode current mechanism responsible for 1/fnoise was isolated. It was found that 1/fnoise is independent of photocurrent and diffusion current but is linearly related to surface generation current. It is proposed that 1/fnoise in reverse-biased (Hg, Cd)Te photodiodes is a result of modulation of the surface generation current by fluctuations in the surface potential.     

High frequency performance of Si/sub 1-x/Ge/sub x//Si/sub 1-y/Ge/sub y//Si/sub 1-x/Ge/sub x/ HBTs

The results of a theoretical study of the performance of high speed SiGe HBTs is presented. The study includes a group of SiGe HBTs in which the Ge concentration in the base is 20% higher than that in the emitter and collector (i.e. y=x+0.2). It is shown that the composition dependences of f/sub T/ and the F/sub max/ are non-monotonic. As the Ge composition in the emitter and collector layers is increased, f/sub T/ and f/sub max/ first decrease, then remain constant and finally increase to attain their highest values.<>     

High-performance, metamorphic In/sub x/Ga/sub 1-x/As tunnel diodes grown by molecular beam epitaxy

Thin In/sub x/Ga/sub 1-x/As tunnel junction diodes having compositions from x=0.53 to 0.75 that span a range of bandgap energies from 0.74 to 0.55 eV, were grown on InP and metamorphic, step-graded In/sub x/Al/sub 1-x/As/InP substrates using molecular beam epitaxy and evaluated in the context of thermophotovoltaic (TPV) applications. Both carbon and beryllium were investigated as acceptor dopants. Metamorphic tunnel diodes with a bandgap of 0.60 eV (x=0.69) using carbon acceptor doping displayed highest peak current densities, in excess of 5900 A/cm/sup 2/ at a peak voltage of 0.31 V, within a 200 /spl Aring/ total thickness tunnel junction. Identically doped lattice-matched tunnel diodes with a bandgap of 0.74 eV exhibited lower peak current densities of approximately 2200 A/cm/sup 2/ at a higher peak voltage of 0.36 V, consistent with the theoretical bandgap dependence expected for ideal tunnel diodes. Specific resistivities of the 0.60 eV bandgap devices were in the mid-10/sup -5/ /spl Omega/-cm/sup 2/ range. Together with their 200 /spl Aring/ total thickness, the electrical results make these tunnel junctions promising for TPV applications where low-resistance, thin metamorphic tunnel junctions are desired.     

GaAs/Al/sub x/Ga/sub 1-x/As quantum well infra-red photodetectors with cutoff wavelength lambda /sub c/=14.9 mu m

The longest wavelength quantum well infra-red photo-detector (QWIP) ever measured with a cutoff wavelength of lambda /sub c/=14.9 mu m is demonstrated when cooled to 10 K. Prospects for even longer wavelength detectors are promising.<>     

The origin of hillocks in (Hg, Cd)Te grown by MOVPE

Dimethylcadmium, a precursor for the metalorganic vapor phase epitaxy of mercury cadmium telluride, has been shown to react with gallium arsenide to form trimethylarsine and dimethylarsine. An analogous reaction occurs between di-iso-propyltelluride and gallium arsenide to form iso-propylarsine and di-iso-propylarsine. It is proposed that if these reactions remove sufficient arsenic from a gallium arsenide substrate, metallic droplets will form on the wafer surface thereby creating the nucleation sites for hillocks. Analogous reactions have been observed between the precursors and a range of other substrates which can in turn be used to explain the origin of hillocks in epitaxial layers grown onto these materials.     

Hg1—xCdxTe的远红外透射光谱与晶格振动

采用傅里叶变换红外光谱仪，在４．２～３００Ｋ、２０～３５０ｃｍ－１范围测量了Ｈｇ１－ｘＣｄｘＴｅ的远红外透射光谱，研究了剩余射线吸收带两侧样品的吸收行为．除了单声子及双声子模外，还观察到杂质能级和由杂质导致的振动模     

Band offsets in Zn 1−x Cd x Te/ZnTe single-quantum-well structures grown by molecular-beam epitaxy on GaAs(001) substrates

ZnTe heteroepitaxial layers and ZnTe/Zn _1?x Cd _x Te/ZnTe strained quantum-confinement structures grown by molecular-beam epitaxy on GaAs(001) were studied by low-temperature cathodoluminescence spectroscopy and current-relaxation deep-level transient spectroscopy (DLTS). A peak related to electron emission from the ground size-quantization level in the conduction-band was observed in the DLTS spectra of quantum-confinement structures. The conduction-band offset parameter Q _C was determined from the DLTS and cathodoluminescence data. For Zn _1?x Cd _x Te/ZnTe single-quantum-well structures with x=0.2–0.22, Q _C equals 0.82 ± 0.05. The effect of internal elastic strain on the band offsets and Q _C at the Cd _x Zn _1?x Te quantum well interfaces was calculated; the results of calculations agree well with experimental data.     

Hg1-xCdxTe metal-semiconductor-metal (MSM)photodetectors

Metal-semiconductor-metal (MSM) detectors with active layers of Hg _1-xCd_xTe (x=0.62-0.74) and electrode spacings of 2, 4, and 6 μm have been fabricated and characterized. Direct-current measurements have shown a low dark current and high responsivity from 0.15 to 1.5 A/W at 10-V bias. The lowest values of dark current (0.16 mA cm²) were obtained for detectors which incorporated an overlayer of CdTe. For detectors without the overlayer, increasing the Cd mole fraction resulted in a decrease in the dark current and a reduction in the 300-nm responsivity. Measurements of frequency response for these detectors show a maximum loss of 8 dB to 20 GHz. These results compare favorably with high-performance MSM detectors based on In_0.53Ga_0.47As with a lattice-matched barrier layer of In_0.52Al_0.48As