Velocity auto-correlation and hot-electron diffusion constant in GaAs and InP

Auto-correlation functions of the fluctuations in the electron velocities transverse and parallel to the applied electric field are calculated by the Monte Carlo method for GaAs and InP at three different values of field strength which are around three times the threshold field for negative differential mobility in each case. From these the frequency-dependent diffusion coefficients transverse and parallel to the applied field and the figure of merit for noise performance when used in a microwave amplifying device are determined. The results indicate that the transverse auto-correlation functionC _t (s) falls nearly exponentially to zero with increasing intervals while the parallel functionC _p (s) falls sharply, attains a minimum and then rises towards zero. In each case a higher field gives a higher rate of fall and makes the correlation functions zero within a shorter interval. The transverses diffusion coefficient falls monotonically with the frequency but the parallel diffusion coefficient generally starts with a low value at low frequencies, rises to a maximum and then falls. InP, with a larger separation between the central and the satellite valleys, has a higher value of the low frequency transverse diffusion coefficient and a lower value of its parallel counterpart. The noise performance of microwave semiconductor amplifying devices depends mainly on the low frequency parallel diffusion constant and consequently devices made out of materials like InP with a large separation between valleys are likely to have better noise characteristics.     

Carrier freezeout in n-on-p Hg0.7Cd0.3Te photodiode and acceptor level determination

0.7 Cd_0.3Te photodiodes at temperatures lower than 25 K. The freezeout was seen under the conditions that interband tunneling dominates the current in the photodiode and that avalanche ionization does not take place. These conditions are fulfilled at temperatures lower than 25 K and reverse bias voltages around 3 V. An acceptor level of about 4 meV was determined for p-type Hg_0.7Cd_0.3Te with N_A-N_D∼10¹⁶ cm^-3 from the temperature dependence of the photodiode resistance governed by carrier freezeout. The difficulties in observation of carrier freezeout in Hg_1-xCd_xTe with a larger composition ratio x or higher doping concentration are discussed. Received: 21 November 1996/Accepted: 15 April 1997     

The performance of Hg1−x Zn x Te photodiodes

This paper considers the Hg_1–x Zn _x Te alloy system as a potential material for the fabrication of infrared photodiodes. The influence of different junction current components (diffusion, tunneling and depletion layer currents) on the R ₀ A product of n⁺-pHg_1–x Zn _x Te photodiodes is analysed. The upper theoretical limits of the R ₀ A product and detectivity are determined. Results of calculations are compared with experimental data reported by other authors and those measured in our laboratory. Preliminary results on related technology and the properties of Hg_1–x Zn _x Te prepared by the ion-etching technique are presented.     

Low-temperature hot-electron energy relaxation in Hg0.8Cd0.2Te in extreme-quantum-limit magnetic fields

Energy relaxation time of hot electrons in Hg_0.8Cd_0.2Te at a lattice temperature of 1.5 K is calculated for quantizing magnetic flux densities of 4 and 6 T considering acoustic scattering via deformation potential and piezoelectric couplings. Band nonparabolicity, nonequipartition of phonons, screening of the scattering rates due to carrier space charge, and low-temperature broadening of the Landau level are incorporated. The calculated results agree qualitatively with experimental data.     

Experimental studies on low frequency noise of Hg0.8Cd0.2 Te photoconductors

Combined with the measurements of material characteristic parameters, detector function parameters and their temperature relation, a series of new noise experimental results on Hg_0.8Cd_0.2 Te photoconductor are obtained. The Hooge parameter from these measurements ranges from 1.7 x 10⁻³ to 8.7 x 10⁻⁵ for temperatures 90–300 K. The 1/ƒ noise spectrum increases with increasing background emission, which cannot be explained by Hooge's empirical formula. The 1/ƒ noise is less than the lower limit calculated by existing theory.     

Non-equilibrium generation-recombination noise in InGaAs/InP photodiodes

We report on temperature (77 to 300 K) and voltage dependent low frequency (100 Hz to 100 kHz) noise behavior of InGaAs/InP photodiodes in non-equilibrium steady state. In addition to common white, 1/f, and Lorentz noise we are able to observe for the first time minima and maxima in the photocurrent noise spectra. The recombination of a pair of free carriers through a recombination center at the heterointerface provides the correlation between the electron and hole ensembles necessary to explain the observed noise reduction.     

分子束外延HgCdTe材料的光致发光研究

报道了分子束外延生长 Ｈｇ０．６８ Ｃｄ０．３２ Ｔｅ 材料的光致发光测量结果。研究了原生样品和退火处理样品、以及氮离子注入样品的低温光致发光特征。对光致发光的测试结果进行拟合得到的禁带宽度, 与用红外透射谱得到的薄膜禁带宽相近; 其半峰宽和带尾能量较小, 显示了较高的薄膜质量。样品经过退火后带尾能量降低, 双晶衍射的半峰宽也有明显的变窄     

Vacancy noise measurements in metals: Calculation of the power spectrum

Fluctuations in the number of vacancies in metals in thermal equilibrium lead to resistivity fluctuations. Analysis of these fluctuations permits measurement of both formation and migration enthalpy of the vacancies. The power spectrum of the fluctuations is calculated using a series of statistically independent pulses. It can be derived from the diffusion equation for any geometry of the vacancy sinks. Vacancy diffusion to the surface of a thin plate or of a sphere are treated as examples. The measurability of vacancy noise is assessed. It should also be possible to measure vacancy noise during irradiation. It is predicted that correlated vacancy creation, which may occur during irradiation, will cause an increase in the power spectrum.     

Contact versus bulk noise in resistive layers

General formulae are derived to calculate the noise generated by a resistor of arbitrary shape. Contact and bulk noise have been taken into account. By calculating a particular example it will be shown that the influence of the contact and bulk noise can be changed by varying the resistor's shape.     

碲镉汞材料中Hg空位缺陷的第一性原理研究

利用基于第一性原理的全电子势线性缀加平面波方法计算了在碲镉汞材料中Hg空位所引起的晶格弛豫以及空位对周围原子成键机制的影响.通过成键过程中电荷密度的变化以及电荷转移的讨论，论述了碲镉汞材料Hg空位引起的弛豫以及这种弛豫产生的主要原因.通过态密度的计算和分析，发现Hg空位的形成将导致第一近邻阴离子Te的5s态能量向高能端移动了055eV，并借助Te 5s态电荷密度与成键电荷密度的计算结果，分析了引起该能态能量平移的主要原因.通过带边态密度变化以及Kohn-Sham(KS)单电子能级的计算和分析，得出了Hg 关键词： 碲镉汞 Hg空位 线性缀加平面波方法     

Magnetic quantum oscillations in the photovoltaic effect of Cd0.24Hg0.76Te

The first experimental evidence of magnetic quantum oscillations in the photovoltaic effect is reported. Experiments were carried out with the p?n junction in Cd_0.24Hg_0.76Te placed in a quantizing magnetic field. The oscillations are related with the interband Γ₈ → Γ₆ magnetoabsorption transmissions. The discrepancy between experimental data and theory is explained by the effect of the p?n junction electric field on the magneto- absorption behaviour.     

Observation of a new gettering mechanism in (Hg,Cd)Te

A new gettering mechanism is proposed for substitutional impurities which diffuse by an interstitial process. In this mechanism, an externally imposed gradient of self interstitials generates a gradient in impurity interstitials leading to the segregation of fast diffusing impurities to low interstitials, high vacancy regions. Data are presented to support this model in (Hg, Cd)Te alloys, as well as explicitly rule out gettering by dislocations, by segregation to precipitates, or by enhanced solubility arising from the interaction of the impurity with a varying Fermi level.     

On the activation energy of the electron liquid in Hg0.8Cd0.2Te

Recently we have shown that a magnetic field induced electron (Wigner) condensation takes places in Hg_0.8Cd_0.2Te. The correlated electrons behave like a viscous liquid with activated mobility [1]. We present the activation energy of the mobility at magnetic fields up to B = 20 T. The experimental data show that the strong increase of the activation energy with B at low fields slow down and even seems to saturate at magnetic fields above 20 T. Qualitatively this behaviour is expected for a magnetic field induced electron liquid.     

Computer simulation of non-cooled long-wavelength multi-junction (Cd,Hg)Te photodiodes

A numerical analysis of long-wavelength multi-junction photodiodes constructed from Cd_xHg_1−xTe heterostructures is performed. The standard Newton iterative scheme is applied to solve the non-linear system of continuity equations and the Poisson equation. All quantities are expressed as a function of electric potential and quasi-Fermi levels. Results of computations are presented in the form of maps and plots illustrating spatial distributions of electrical potential and responsivity. Such an illustration enables us to explain the effect of reverse sign of the photovoltage occurring in photoelectric devices being manufactured.     

Magnetic-field induced metal-insulator transition in InSb and Hg0.79Cd0.21Te at very low temperatures

We report measurements of the transverse and Hall resistivities and of the nonlinear current-voltage characteristics in low compensation n-type InSb and Hg_0.79Cd_0.21Te samples at low temperatures (down to 0.08 K) and high magnetic fields. The results for the two materials are very similar and establish that the magnetic-field-induced metal-insulator transition in these narrow gap semiconductors is identical.     

Light switching at a prism-liquid crystal interface. A new sensor for magnetic fields

Light beam propagation at a prisms-liquid crystal interface is studied both theoretically and experimentally. Our results suggest the possibility of employing such an interface as an element while designing optical sensors for magnetic fields. A comparison between the data of a theoretical model based on the Berreman formalism and the experimental results is presented.     

Defect related luminescence in Hg0.2Cd0.8Te nano- and micro-crystals grown by the solvothermal method

The photoluminescence (PL) properties of nano- and micro-crystalline Hg_1?xCd_xTe (x≈0.8) grown by the solvothermal method have been studied over the temperature range 10–300 K. The emission spectra of the samples excited with 514.5 nm Ar⁺ laser consist of five prominent bands around 0.56, 0.60, 0.69, 0.78 and 0.92 eV. The entire PL band in this NIR region is attributed to the luminescence from defect centers. The features like temperature independent peak energy and quite sensitive PL intensity, which has a maximum around 50 K is illustrated by the configuration coordinate model. After 50 K, the luminescence shows a thermal quenching behavior that is usually exhibited by amorphous semiconductors, indicating that the defects are related to the compositional disorder.     

脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

 利用光学金相显微镜对TEA-CO₂脉冲强激光辐照的Hg_0.8Cd_0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J，能量密度为937.5 J/cm²的强激光辐照下，晶片表面呈现出熔融迹象和大量的微裂纹，微裂纹密度从激光辐照区中心向外逐渐减少，裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加，晶片表面熔融更加剧烈，裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。