R. N. Bicknell

High resolution electron microscope study of epitaxial CdTe‐GaAs interfaces

CdTe films have been grown on (100) GaAs substrates with two different epitaxial relations: (111)CdTe∥(100)GaAs and (100)CdTe∥(100)GaAs. High resolution electron microscope observation of these two types of interfaces was carried out in order to investigate the role of the substrate surface microstructure in determining which type of epitaxy occurs. The interface of the former type shows a direct contact between the CdTe and GaAs crystals, while the interface of the latter type has a very thin layer (∼10 A in thickness), which is most likely an oxide, between the two crystals. These observations suggest that the GaAs substrate preheating cycle prior to CdTe film growth is crucial in determining which type of epitaxy occurs in this system.

Growth of high mobility n‐type CdTe by photoassisted molecular beam epitaxy

We report details of the successful controlled substitutional doping of CdTe films with indium. These n‐type films were prepared using a new technique, photoassisted molecular beam epitaxy, in which the substrate is illuminated during the deposition process. In the present work, an argon ion laser was used as an illumination source. The incident light was found to produce immediate and significant changes in the electrical properties of the films. In particular, highly activated n‐type CdTe:In layers resulted.

Cd1−xMnxTe‐CdTe multilayers grown by molecular beam epitaxy

Single‐crystal multilayers of the dilute magnetic semiconductor Cd1−x Mnx Te (x∼0.2) alternating with CdTe have been successfully grown for the first time using the molecular beam epitaxy technique. Four sets of superlattices have been prepared consisting of 14, 60, 90, and 240 double layers of average thickness 460, 140, 75, and 37 A, respectively. Each set consists of two samples grown simultaneously using 7×15×1‐mm thick (0001) sapphire substrates onto which 5.0‐μm‐thick CdTe buffer layers were first deposited. X‐ray diffraction techniques were employed to verify that epitaxy had been achieved and to obtain the average lattice constant of each of the multilayer structures. X‐ray diffraction satellites were observed on both sides of the (111) diffraction peak of the superlattices composed of 14 and 60 alternating layers, respectively, which allowed an accurate estimate of the superlattice period, or double‐layer thickness, for these samples. Results of UV reflectance studies and photoluminescence experi...

Photoluminescence of CdTe: A comparison of bulk and epitaxial material

Photoluminescence (PL) studies of bulk and epitaxial CdTe samples obtained from several sources are discussed. Steady state PL measurements were carried out at temperatures ranging from 16–300 K. The effects of surface preparation, substrate temperature, and film thickness were studied in detail for homoepitaxial films grown on the (111)A and (100) planes of CdTe. PL studies of epitaxial CdTe films grown on (0001) sapphire by molecular beam epitaxy (MBE), by hot wall MBE, and by metal‐organic chemical vapor deposition (MOCVD), and on the (111)B and (100) planes of GaAs by MBE have also been completed. The CdTe epilayers on sapphire and GaAs substrates typically display a bright PL spectrum dominated by the near edge peak at 1.58 eV (77 K). In addition, a number of films exhibit a near edge peak at 1.503 eV at 300 K, which is indicative of high quality epitaxy and which allowed direct measurement of the room temperature band gap of CdTe. PL studies of epitaxial Cd1−x MnxTe films grown by MBE on 5.0 μm thic...

Growth of (100)CdTe films of high structural perfection on (100)GaAs substrates by molecular beam epitaxy

Growth of epitaxial (100) CdTe films on (100) GaAs substrates by molecular beam epitaxy is discussed. X‐ray diffraction, UV reflectance, photoluminescence, and transmission electron microscopy techniques were employed to characterize the film specimens. The high structural perfection of the layers was evidenced by line dislocation densities of ≤104/cm2 at the free surface of films ≂6.6 μm thick and by measurable excitonic photoluminescence (∼1.504 eV) at room temperature. The CdTe epilayers were smooth and mirrorlike in appearance.

Growth of CdTe films on sapphire by molecular beam epitaxy

Results of initial attempts to grow cubic‐phase CdTe films on sapphire by molecular beam epitaxy are reported. Depositions have been completed on (1102) R‐plane, (1210) A‐plane, and (0001) basal plane substrates. Substrate temperatures in the range 260–350 °C were employed along with deposition rates of 1.5–7.5 A/s. Depositions on (1102) sapphire generally produced films containing some elements of the hexagonal phase, as disclosed by x‐ray diffraction and UV reflectance measurements. Sharp cubic‐phase epitaxy was obtained for thick (∼5 μm) CdTe films grown on (1210) and (0001) sapphire substrates. The epitaxial films are smooth and mirrorlike in appearance. Nomarski micrographs show a featureless CdTe surface.

p‐type CdTe epilayers grown by photoassisted molecular beam epitaxy

We report the first successful substitutional doping of CdTe films with antimony. These p‐type epilayers were prepared using a new technique, photoassisted molecular beam epitaxy, in which the substrate is illuminated during the film deposition process. Illumination was found to produce immediate and favorable changes in the electrical properties of the CdTe:Sb films such that highly activated p‐type layers resulted. CdTe:Sb films grown under similar conditions, but in the absence of illumination, were found to be insulating.

Stimulated emission from a Cd1−xMnxTe‐CdTe multilayer structure

In this letter we report the first observation of stimulated emission from an optically pumped Cd1−xMnxTe‐CdTe multilayer structure. This new laser structure was grown by molecular beam epitaxy and consists of an active superlattice (SL) region containing 25 CdTe quantum wells (Lz∼150 A) alternating with 24 Cd1−xMnxTe (x∼0.45) barriers (LB∼50 A). The SL is sandwiched between thicker Cd1−xMnxTe cladding layers. The substrate consists of a 2‐μm‐thick buffer layer of CdTe on GaAs. The Cd1−xMnxTe‐CdTe SL lasers operate at 763–766 nm when optically pumped at ∼25 K with a cavity‐dumped argon ion laser which emits 4‐ns light pulses (514.5 nm) at a repetition rate of 3.8 MHz. The onset of laser action occurs at a peak pump power density of about 1.35×104 W/cm2. The mode spacing of the emitted laser radiation is in reasonable agreement with the spacing expected from measured cavity dimensions of the Cd1−xMnxTe‐CdTe multilayer.

Magnetically tunable diluted magnetic semiconductor (Cd, Mn)Te quantum well laser

We report the first observation of strong magnetic field tuning of laser emission from Cd1−xMnxTe/Cd1−yMnyTe multiple quantum well structures. The spectral peak of the stimulated emission shifts to lower energy with increasing field at a rate of 3.4 meV/T to a maximum shift of 34 meV at 10 T. This is about five times slower than in bulk Cd1−xMnxTe with a comparable x value. Stimulated emission was observed for samples cooled to 1.9 K when optically pumped with a Nd:YAG laser.

Properties of Cd1−xMnxTe–CdTe superlattices grown by molecular beam epitaxy

Single‐crystal multilayers of the dilute magnetic semiconductor Cd1−xMnxTe alternating with CdTe have been successfully grown for the first time by MBE. Experimental techniques used to prepare the various superlattice samples are described. Results of x‐ray diffraction and photoluminescence film characterization experiments are also discussed.