E. Finkman

Intersublevel transitions in InAs/GaAs quantum dots infrared photodetectors

Thermal generation rate in quantum dots (QD) can be significantly smaller than in quantum wells, rendering a much improved signal to noise ratio. QDs infrared photodetectors were implemented, composed of ten layers of self-assembled InAs dots grown on GaAs substrate. Low temperature spectral response shows two peaks at low bias, and three at a high one, polarized differently. The electronic level structure is determined, based on polarization, bias, and temperature dependence of the transitions. Although absorbance was not observed, a photoconductive signal was recorded. This may be attributed to a large photoconductive gain due to a relatively long lifetime, which indicates, in turn, a reduced generation rate.Thermal generation rate in quantum dots (QD) can be significantly smaller than in quantum wells, rendering a much improved signal to noise ratio. QDs infrared photodetectors were implemented, composed of ten layers of self-assembled InAs dots grown on GaAs substrate. Low temperature spectral response shows two peaks at low bias, and three at a high one, polarized differently. The electronic level structure is determined, based on polarization, bias, and temperature dependence of the transitions. Although absorbance was not observed, a photoconductive signal was recorded. This may be attributed to a large photoconductive gain due to a relatively long lifetime, which indicates, in turn, a reduced generation rate.

The exponential optical absorption band tail of Hg1−xCdxTe

The optical absorption edges of Hg0.71Cd0.29Te and CdTe were measured over the temperature range 80≤T≤300 K. The refractive indices of these materials are determined over a large energy range at T=300 K and their dispersion relation is given. The absorption band tail of Hg1−xCdxTe has an exponential shape. Its slope increases with decreasing temperature. It is suggested that this tail is not caused by permanent lattice disorder but is a material property. An empirical expression for the absorption coefficient as a function of temperature and composition is derived. Using this expression, the zero‐intercept cut‐on energy of the infrared transmission spectrum at room temperature is used to define the composition for any desired thickness of Hg1−xCdxTe sample.

Recombination mechanisms in p‐type HgCdTe: Freezeout and background flux effects

The recombination mechanisms in HgCdTe are analyzed. Detailed expressions for the radiative lifetime are presented, taking into account recent measurements of the absorption coefficient. In p‐type material, carrier freezeout is shown to increase the lifetime exponentially for the radiative and the Auger processes at low temperatures. The effect of background flux is introduced, taking into account its variation with temperature due to the change in energy gap. Lifetime measurements on p‐type samples are in good agreement with combined Auger 7 and radiative mechanisms, where the Auger process is more effective for low x values. Highly compensated materials are dominated by the Shockley–Read recombination. For all samples, the intrinsic region is controlled entirely by the Auger process.

Dependence of the refractive index of AlxGa1−xN on temperature and composition at elevated temperatures

The refractive index of hexagonal AlxGa1−xN at room temperature and its temperature dependence at elevated temperatures have been determined with high accuracy by spectroscopic ellipsometry. Measurements have been conducted on samples with aluminum molar fractions ranging from 0% to 65% and at temperatures between 290 and 580 K. The refractive index in the transparent spectral region has been determined as a function of photon energy, using the Kramers–Kronig relations with suitable approximations, and applying a multilayer model. An analytical expression for the composition and temperature dependent refractive index in the transparent region, above room temperature, has been obtained. The refractive index has been found to increase with increasing temperature. The shift of the refractive index is strongest for GaN and decreases for AlGaN with increasing aluminum molar fraction. The impact on the properties of GaN based waveguides is illustrated by a slab waveguide calculation.

Electrical properties of shallow levels in p‐type HgCdTe

Electrical measurements of gold‐doped and undoped p‐type Hg1−xCdxTe with x≂0.22 are reported and two models based on two shallow acceptor levels for the analysis of the Hall data are developed. One model assumes two independent acceptors and the other assumes one divalent acceptor. The models yield ionization energies of 12.5±2 and 2–5 meV. The concentration of the compensating donors is of the order of the hole concentration. Arguments are given in order to assign these levels to established point defects.

Two‐electron conduction in N‐type Hg1−xCdxTe

The results of galvanomagnetic measurements in N‐type Hg1−xCdxTe, as a function of magnetic field for the compositions x≃0.215 and x≃0.29 and over the temperature range 15⩽T⩽300 K are reported. A unified model is proposed which fits the magnetic field dependence of both the conductivity and the Hall coefficient. The most significant feature of the model is that two types of electrons are contributing to the transport properties and are responsible for the magnetic field dependence of the conductivity and the Hall coefficient. The two sets of electrons have mobilities which at the lowest measured temperature (15 K) differ by up to two orders of magnitude, and have concentrations which are of the same order of magnitude.

Growth of CdTe single crystals

Abstract Pure CdTe single crystals were grown from the melt under different Cd(Te) overpressures. In order to characterize the material, some electrical and optical properties were measured.

Realization of Si1−x−yGexCy/Si heterostructures by pulsed laser induced epitaxy of C+ implanted pseudomorphic SiGe films and of a-SiGeC:H films deposited on Si(100)

Si 1-x-y Ge x C y /Si heterostructures are realized by pulsed laser induced epitaxy (PLIE) from C + implanted pseudomorphic Si 0.84 Ge 0.16 films and from hydrogenated amorphous SiGeC films deposited on Si(100). The laser treated samples are examined by electron channelling, energy dispersive X-ray analysis, Rutherford backscattering spectroscopy and ion channelling, X-ray diffraction, secondary ion mass spectrometry, and infrared and Raman spectroscopy. We show that PLIE occurs when the laser fluence exceeds a threshold for which the liquid-solid interface reaches the crystalline substrate at each laser pulse. Above this threshold, germanium and carbon atoms diffuse inside the melted layer, and carbon incorporation in substitutional sites increases with the laser fluence and the number of pulses. The resulting SiGeC layers are pseudomorphic.

Determination of band‐gap parameters of Hg1−xCdxTe based on high‐temperature carrier concentration

The temperature dependence of the carrier concentration of Hg1−xCdx Te at elevated temperatures is used to determine its band parameters near the bandedge. The electron concentration is calculated by using the Kane model (k⋅p method), and is fit to observed values derived from measurements of the Hall coefficient in the near‐intrinsic region. This procedure results in expressions for the following parameters: the band‐gap Eg and its dependence on temperature and composition; Kane’s interband‐coupling matrix element and the heavy‐hole effective mass ratio. Modified values of the intrinsic carrier concentration are calculated using these parameters.

Surface recombination velocity of anodic sulfide and ZnS coated p-HgCdTe

The surface recombination velocity s has been determined for Hg1−xCdxTe (x∼0.2) for two different surface passivations: (i) anodic sulfide with an overcoating of ZnS and (ii) ZnS coating on freshly etched samples. The method used was photoelectromagnetic effect, in which a magnetic field is applied perpendicular to the diffusion current of optically generated injected carriers. Analysis of the magnetic field dependence of the resulting current can yield s, as well as carrier mobility, lifetime, etc. The temperature dependence of s is very similar for the two passivations at temperatures higher than 50 K, and is increasing with decreasing temperature. At low temperatures s continues to rise for ZnS passivation and stays flat for the native anodic sulfide. Two activation energies are determined: 12.5±1.5 meV at temperatures higher than 60 K, and 2.3±0.2 meV at temperatures lower than 30 K. The high‐temperature activation energy is identical for both passivations. It is concluded that the same surface traps ...