M. Boukerche

Molecular beam epitaxial growth of CdTe and HgCdTe on Si (100)

CdTe has been grown on Si(100) by molecular beam epitaxy. Two orientations can be obtained: (111)B CdTe when the CdTe is deposited directly on the Si(100) substrates, and (100)CdTe when an intermediate layer of ZnTe is grown first. The (111)B oriented layers are made of two domains which are rotated by 90°. A layer with only one domain can be grown on Si(100) misoriented by 8°, but the best misorientation for this purpose still needs to be found. These layers were characterized by reflection high‐energy electron diffraction, photoluminescence spectroscopy, scanning electron microscopy, and x‐ray diffraction. Hg1−xCdxTe has also been grown by molecular beam epitaxy on (111)B CdTe on Si(100).

Minority‐carrier lifetime in p‐type (111)B HgCdTe grown by molecular‐beam epitaxy

Measurements of electron lifetime have been carried out on unintentionally doped layers of (111)B Hg1−xCdxTe (0.216<x<0.320), p‐type as‐grown by molecular‐beam epitaxy. The temperature dependence of the bulk lifetime is explained in terms of the Shockley–Read recombination mechanism for the extrinsic region. The samples have shown a deep level close to midgap. The surface recombination seen in two of the samples is accounted for. Some samples show clearly Auger‐limited recombination at high temperatures. From the values of τn0 and τp0 of two samples the trap level appears to have a donorlike character.

The doping of mercury cadmium telluride grown by molecular‐beam epitaxy

The electrical properties of the mercury cadmium telluride semiconductor material grown by the molecular‐beam epitaxy are reviewed. The doping effects linked to the growth conditions, as well as the influence of indium or lithium incorporation are discussed. The results on doping by silicon, arsenic, and antimony are presented. It will be shown that all the impurities studied interact primarily with the metal site. It will confirm that the growth occurs under very rich tellurium conditions.

Molecular beam epitaxial growth of high quality HgTe and Hg1−xCdxTe onto GaAs(001) substrates

HgTe and Hg1−xCdxTe epilayers have been grown for the first time onto GaAs (001) substrates by molecular beam epitaxy (MBE). A thin MBE CdTe buffer has been first deposited. The (001) orientation of the substrate is conserved during the growth. Despite the important lattice mismatch in situ electron diffraction experiments showed that the films have a high crystal quality. Hall measurements carried out on these layers confirm their high quality because they exhibited high electron Hall mobilities. We have shown also, using a Hall mobility profiling etching technique, that the interfacial disorder zone in a HgCdTe layer deposited on a 0.4‐μm CdTe buffer layer could be less than 1 μm. This first report of very good electrical performances for Hg1−xCdxTe layers grown onto GaAs substrates is highly promising for growth and device applications regarding this material and related superlattices.

Electrical properties of Li‐doped Hg1−xCdxTe(100) by molecular beam epitaxy

p‐type doping of HgCdTe(100) layers with lithium during growth by molecular beam epitaxy is reported. Hall measurements have been performed on these layers between 300 and 30 K. The Li concentration is found to increase with the Li cell temperature. Li‐doped HgCdTe layers are estimated to have very shallow acceptor levels. Acceptor concentrations as high as 8×1018 cm−3 have been achieved. At low doping levels, due to residual donors, layers show compensation. Incorporation coefficient of Li close to 1 and almost 100% electrical efficiency for Li in molecular beam epitaxy HgCdTe layers were observed. However, Li is found to diffuse rapidly in HgCdTe layers grown by molecular beam epitaxy.

Indium doping of HgCdTe layers during growth by molecular beam epitaxy

Successful n‐type doping of HgCdTe layers with indium during growth by molecular beam epitaxy is reported for the first time. The indium concentration is found to increase with the In flux. The doping level reaches around 1018 cm−3, which is nearly two orders of magnitude more than what can be achieved by stoichiometry deviation in as‐grown samples. In the range studied, the electrical efficiency is substantial and decreases with increasing In atomic concentration. The experimental measurements are in agreement with a model suggesting that indium, which is not singly ionized, precipitates as In2Te3 and that the native acceptor defect concentration remains approximately constant. n‐type doping is shown to be possible for a wide range of alloy concentrations. Good electron mobilities in the alloy are presented for the doping concentrations studied. This technique will greatly enhance the potential of molecular beam epitaxy for device applications of this material.

HgTe/CdTe superlattices grown by molecular beam epitaxy

Abstract In this paper we present results concerning the optical absorption in HgTe-CdTe superlattices. We confirm the narrowing of the superlattice band-gap (the increase of cut-off wavelength, λc) compared to the band gap of the equivalent Hg1−xCdxTe alloy. We show also, as predicted by the theory, an increase of the cut-off wavelength of the superlattice when the HgTe layer thickness increases. At 300K, the agreement between theory and experiment is fairly good if we consider the onset of the absorption. The λc tail shifting towards shorter wavelengths could be explained by the interdiffusion between HgTe and CdTe layers. At 30K, no important change in the I.R. absorption is noticed for all the superlattices. We present for the first time a superlattice exhibiting an absorption in the 8–12 μm window. We have carried out Hall measurements on several superlattices and present for the first time transport properties on these alternate microstructures. The most important features concern the unexpected and not yet understood very high hole mobilities at 10K.

Electrical properties of intrinsic p‐type shallow levels in HgCdTe grown by molecular‐beam epitaxy in the (111)B orientation

The electrical properties of the unintentionally doped p‐type HgCdTe material as grown in the (111)B orientation by molecular‐beam epitaxy are revised. The analysis of the Hall coefficient in the whole temperature range with a model based on the two‐band nonparabolic Kane model, a fully ionized compensating donor concentration, and two independent discrete acceptor levels is presented. The donor compensation is found to be much lower than before, in agreement with the latest study of extrinsic doping by indium. A defect level with an energy of 30 to 50 meV is found necessary to explain properly some of the crystals’ data. The results of a three‐carrier band modeling of the Hall constant versus field are also presented for one sample and are in very good agreement with the expected band structure of the material. These results show that important improvements have been made recently in the control of stoichiometry during growth.

II–VI semiconductor compounds: New superlattice systems for the future?

Abstract In this paper we present a general survey of growth and characterization of HgTe-CdTe superlattices. From very recent experiments, done by infrared absorption and infrared photoluminescence, we compare the experimental values obtained for the energy gap, E g , with those calculated theoretically and we show that the agreement is fairly good. We report also on the interdiffusion between layers. We comment on the temperature independence of E g from infrared absorption measurements and the very high hole mobilities observed in p-type superlattices, phenomena unpredicted by current theoretical models. From all of these results, it appears that HgTe-CdTe superlattices could be important materials for future device applications.

Growth of Hg1−xZnxTe by molecular beam epitaxy on a GaAs(100) substrate

We report for the first time the growth and characterization of n‐type and p‐type Hg1−xZnxTe layers grown by molecular beam epitaxy on GaAs (100) substrates. The HgZnTe grown over either (111)CdTe‖‖(100)GaAs or (100)CdTe‖‖(100)GaAs buffer layers preserved the orientation of the buffer. Electron diffraction and electrical characterization demonstrate the HgZnTe layers to be comparable to high quality HgCdTe of the same cut‐off frequency. Since the layers exhibit cut‐off wavelengths in far and mid‐infrared range and are of high quality, they appear to be candidates for infrared devices.