J. P. Faurie

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.

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.

Electron transport and cyclotron resonance in [211]-oriented HgTe-CdTe superlattices

We discuss a magnetotransport and magneto‐optical investigation of [211]‐oriented HgTe–CdTe superlattices. Measurements were performed on seven n‐type samples with well widths in the range 41–125 A and energy gaps between 0 and 128 meV. Both magnetotransport and magneto‐optical results give evidence for an additional electron species besides the superlattice electrons and holes usually observed. We show that although these have quasi‐two‐dimensional character, their mobilities are quite sensitive to the superlattice well thickness. These findings are interpreted in terms of band bending and charge transfer from the CdTe substrate into the superlattice. We also discuss the first theoretical calculations of the band structure for [211]‐oriented HgTe–CdTe heterostructures.

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.

Electrical properties of molecular beam epitaxy produced HgCdTe layers doped during growth

Electrical characterizations of n‐ and p‐type mercury cadmium telluride epitaxial layers intentionally doped during their growth by the molecular beam epitaxy technique are reported. The doping by stoichiometry adjustment can produce good mobility material of both n or p semiconductor types. However, p‐type material is feasible only for cadmium fraction (x) greater than 0.2, whereas the n‐type conduction is possible only for x less than 0.3. For the first time in situ doping of HgCdTe by indium is reported. It is incorporated in the material during the growth and behaves as a n‐type dopant. Carrier concentrations up to 1018 cm−3 have been obtained. An indium doped layer having a cadmium fraction of 0.55 was also found to be n‐type.

Nonlinear optical coefficients of Hg‐based superlattices

The first measurement of the third‐order nonlinear optical susceptibility χ(3) in Hg‐based narrow‐gap semiconductor superlattices is reported. Four‐wave mixing experiments were performed at CO2 laser wavelengths on a series of HgTe/CdTe and Hg1−xZnxTe/CdTe superlattices whose energy band gaps are approximately zero at T=0 K. The nonlinearity is believed to due to modulation of the free‐carrier temperature and density by the optical beams. Theoretical estimates of the third‐order nonlinear susceptibility due to this mechanism are in good agreement with the experimental results.

Mercury cadmium telluride junctions grown insitu by molecular‐beam epitaxy

The characterization of n‐isotype mercury cadmium telluride heterojunctions made in situ by molecular‐beam epitaxy is reported first. The cadmium composition of each side is 0.3 for the top material and 0.21 for the bottom. Both sides were doped with indium. Strong rectification with an ideality factor varying from 1.8 to 2.5 is shown. The forward bias occurs when the wide‐band‐gap material is biased negatively. The preliminary results of the first homojunctions made by the same technique are then presented. The cadmium composition was 0.27. The bottom p‐type material was doped by stoichiometric deviation, whereas the top n‐type material was doped with silicon. The device is sensitive to infrared radiation and it is found that the doping concentration is not uniform. We suggest that generation–recombination is limiting the device operation at high temperatures.

Hall and electroreflectance studies of the effects of doping in mercury–cadmium telluride grown by molecular‐beam epitaxy

Hall and electrolyte electroreflectance (EER) measurements have been performed on a series of mercury–cadmium telluride samples grown by molecular‐beam heteroepitaxy on semi‐insulating GaAs substrates and varying from p type to heavily doped n type. Our results show for as‐grown, n‐type samples grown under nearly ideal conditions that the mobilities are high and that the n character is not primarily associated with defects. Our Hall results show that as one departs from nearly ideal growth conditions in order to obtain higher n‐type doping levels, the mobility decreases precipitously. An analysis of the temperature dependence of the mobility suggests that this decrease is associated with a rapid increase in both the number of ionized impurities and the number of neutral scattering centers. Our EER results show that the initial decrease of the mobility is associated with the formation of inhomogeneous strains and, to a lesser extent, both point defects and two‐dimensional structural faults. They also show ...

Role of the crystallographic orientation on the incorporation of indium in HgCdTe epilayers grown by molecular beam epitaxy

In‐doped HgCdTe films have been grown by molecular beam epitaxy (MBE) on CdTe substrates in the (100) crystallographic orientation. They were characterized by Hall and secondary‐ion mass spectroscopy measurements. The results are compared with those of In‐doped HgCdTe layers grown in the (111)B orientation. In the (111)B orientation indium is incorporated in the metal site whereas in the (100) orientation it appears that indium is mainly incorporated interstitially. The results agree with a Te antisite model as a possibility for explaining the electrical behavior of (100) HgCdTe grown by MBE.

Magnetic generation of electrons and holes in semimetallic HgTe–CdTe superlattices

We predict theoretically, on the basis of field‐dependent band structure considerations, that it should be possible to generate a high‐density electron‐hole plasma in semimetallic HgTe–CdTe superlattices simply by applying a magnetic field. When the field is above a critical value, minority carriers should coexist with majority carriers in the zero‐temperature limit, with both densities increasing as B−Bcrit. Experimental confirmation of this unique effect is provided by low‐temperature magneto‐optical data showing the emergence of minority holes in two n‐type superlattices whenever B≥Bcrit.