xCdxTe Films Research Articles

Properties of Hg-based films and superlattices grown by molecular-beam epitaxy

We report the electrical, optical, and structural properties of thin films of HgTe, Hg1−xCdxTe, and Hg1−xMnxTe and superlattices of HgTe–CdTe and Hg1−xMnxTe–HgTe. All of these epitaxial films were deposited by molecular-beam epitaxy. The Hg1−xCdxTe films exhibit large electron Hall mobilities, specular reflectances, and sharp optical absorption edges. The Hg1−xMnxTe films, grown with x values of 0.03 and 0.10, also exhibit excellent optical and electrical properties. The p-type HgTe–CdTe superlattices exhibit large hole mobilities. Superlattices containing alternating layers of Hg1−xMnxTe and HgTe have also been successfully prepared. The Hg1−xMnxTe–HgTe multilayers are the first superlattices containing alternating layers of a Hg-based dilute magnetic semiconductor to be grown by any thin-film technique.

Electrical activity, mode of incorporation and distribution coefficient of group V elements in Hg1−xCdxTe grown from tellurium rich liquid phase epitxial growth solutions

Hg1−xCdxTe films were grown liquid phase epitaxially from tellurium rich solutions containing up to 10 at. % of the group V elements P, As, Sb, and Bi. Chemical analysis of the Te growth solutions and the films was carried out in conjunction with extensive Hall effect measurements on the films subsequent to various annealing treatments under Hg rich and Te rich conditions. Despite the presence of a large concentration of the group V elements in the Te source solution, the maximum concentration of these elements incorporated into the liquid phase epitaxially grown Hg1-xCdxTe appears to vary from <1015cm−3 for Bi up to 1017cm−3 for phosphorus and As implying a distribution coefficient varying from <10−5 for Bi up to 10−3 for P at growth temperature of ∼500° C. This low value of the distribution coefficient for group V elements for growths from Te rich solutions contrasts with the moderately high values reported in the literature to date for growth from Hg rich solutions as well as pseudobinary solutions (Bridgman growth). The widely differing distribution coefficients and hence the solubility of the group V elements for Hg rich and Te rich liquid phase epitaxial solutions is explained on the basis that the activity coefficient of the group V elements in Te rich solutions is probably orders of magnitude lower than it is in Hg rich solutions. Finally, the results of the anneals at 200° C under Hg saturated conditions with and without a 500° C Hg saturated preanneal have indicatedn top conversion in many of the films attesting to the amphoteric behavior of the group V elements in LPE grown Hg1−xCdxTe(s) similar to the previously reported behavior of P in bulk grown Hg0.8Cd0.2Te.

Transmission electron microscopy of liquid phase epitaxial Hg1−xCdxTe layers on CdTe substrates

Epitaxial Hg1−xCdxTe films were grown on (111)A CdTe substrates by the tellurium solvent, horizontal tube slider liquid phase epitaxy technique. Their microstructures were subsequently investigated by both planar and cross-sectional transmission electron microscopy (TEM). Planar TEM showed the top surface of the films to be precipitate free with a general dislocation density &amp;lt;106/cm2 except for localized regions containing high dislocation densities associated with linear surface features on the Hg1−xCdxTe. Cross-sectional TEM showed the interface region to be nonplanar due to meltback during epilayer growth. A three-dimensional dislocation structure was confined to a band in the interface region having a graded Hg composition.

MBE growth of CdTe, Hg1−xCdxTe, and multilayer structures: Achievements, problems, and prospects

In this review the reasons for pursuing MBE (molecular beam epitaxial) growth of multilayer structures involving CdTe and Hg1−xCdxTe films are discussed. One major reason is that the poor structural quality of commercially available CdTe substrate wafers leads to limitations and degradation in structural quality of homoepitaxial CdTe films and Hg1−xCdxTe films grown on CdTe substrates. Double-crystal x-ray rocking curve (DCRC) analysis and x-ray topography have been used to identify intrinsic defects in CdTe which are responsible for this degradation. Progress toward MBE growth of a Hg1−xCdxTe /CdTe/InSb multilayer structure, which avoids the use of CdTe wafers and is based on high-perfection InSb substrates, is described. It is seen that the iterative use of powerful characterization techniques such as DCRC analysis and cross-section transmission electron microscopy (XTEM) is essential to the development of such structures. Major challenges to the approach of MBE to preparation of multilayer structures are considered.

Current Status of thin film HgCdTe: Relationship of Structure and Chemistry to Device Application

ABSTRACTThis paper addresses the current status of thin film HgCdTe and limitations in the currently achievable thin film properties. The emphasis is placed on Hg1−xCdxTe since this material is presently most seriously considered for infrared devices and particularly resistant to high quality film preparation due to large elemental vapor pressure differences. The current status of thin film HgCdTe is reviewed and the various thin film deposition techniques utilized to prepare HgCdTe thin films are compared. Finally, results are reviewed which still support the claim.that the less investigated technique of bias-sputtering, modified to accommodate deposition in a high partial pressure background of Hg vapor, can yield structurally high quality Hg1−xCdxTe films with device-worthy properties. Significant is the fact that the deposition process still provides the simple and systematic control over all relevant film properties without post-deposition treatment. Such control is required to achieve the desired material for device application. As is also reviewed here, this work was one of the first to demonstrate the ability to use low cost foreign substrates for HgCdTe thin film device fabrication.

Open-tube vapor transport epitaxy of Hg1−xCdxTe

A novel set-up for horizontal open-tube vapor transport epitaxy of Hg1−xCdxTe films is described. Mirror-like Hg1−xCdxTe epitaxial layers with thicknesses up to 40 Μm were grown and characterized. The growth temperature ranged from 380 to 550‡C, with growth rates of the order of 0.5–7 Μm per hour. The concentration depth profiles and the optical and electrical properties of relatively uniform films with x≈0.3–0.4 are reported. The process kinetics are studied. A simple model which takes into account the reactions occurring at the boundaries of the epitaxial layer and the interdiffusion in the epilayer is presented and discussed. The model fits the experimentally observed characteristics of the epitaxial growth process. A constant growth rate leading to a linear dependence of film thickness upon deposition time y–yi=ks t is derived. The reaction rate constant k is given by ks=koe−Ea/kT with ko=0.18 cm-sec−1and the energy of activation Ea=1.12 eV.