H. H. Farrell

Structural characterization of GaAs/ZnSe interfaces

We have studied, using reflection high energy electron diffraction (RHEED), the initial growth stages of ZnSe layers grown by molecular beam epitaxy (MBE) on GaAs exhibiting various surface terminations. The structural quality of the ZnSe layers was assessed by transmission electron microscopy (TEM). We have observed a preference for two‐dimensional nucleation on As‐terminated GaAs substrates, whether epitaxial or bulk. On Ga‐terminated surfaces a transitional region of three‐dimensional growth forms initially. The different behaviors may reflect the electronic imbalance present in the growing GaAs/ZnSe interface. While defect free, thin layers of ZnSe are best obtained on As‐terminated GaAs, the initial three‐dimensional growth region on the Ga‐rich surfaces appears to reduce the density of extended faults formed in thick ZnSe layers due to the lattice mismatch with GaAs.

Optical transitions and chemistry at the In0.52Al0.48As/InP interface

We report properties of the InAlAs/InP interface and its formation during growth by organometallic molecular beam epitaxy. Taking advantage of the photoluminescence emission occurring at this type II interface, we were able to directly investigate the interface characteristics for different growth conditions. A shift is observed in the energy of the interface recombination transition which we interpret as evidence of a P‐As exchange effect dependent on the specific growth sequence. This effect was further investigated by growing interfaces with thin layers (InAs, AlAs, AlP) between the InP and InAlAs. The results can be understood in terms of a model based on bond strength considerations. We predicted and demonstrated that the most stable interface is obtained with incorporation of a thin AlP interfacial layer.

Surface stoichiometry effects on ZnSe/GaAs heteroepitaxy

Abstract We describe a simple model, based on counting of valence electrons at the interface, which can predict the surface reconstructions which provide optimal heteroepitaxial growth. Vertical photocurrent measurements on a series of ZnSe/GaAs heterostructures grown by molecular beam epitaxy, using various GaAs surface reconstructions, support the model predictions that surfaces which provide nearly equal number of the constituent atoms for interface bonds produce the highest quality interfaces.

Contactless electrical characterization and realization of p‐type ZnSe

ZnSe is a potentially useful optoelectronic material for applications requiring emission in the blue region of the spectrum. However, such applications necessitate the development of p‐type material, for which reliable ohmic‐contact technology does not exist. To avoid difficulties associated with contact formation while developing p‐type material, we combine two contactless methods, reflectance‐difference spectroscopy and inductive‐coupled radio‐frequency loss to determine carrier type and sheet resistance, respectively. Using this information we have prepared conducting p‐type ZnSe by doping the material during growth with Li.

Reflection high‐energy electron diffraction electron‐stimulated desorption from ZnSe(100)(2×1)‐Se surfaces

The electron‐stimulated desorption (ESD) of Se from ZnSe(100)(2×1) surfaces prepared by molecular‐beam epitaxy (MBE) and monitored with reflection high‐energy electron diffraction is reported. Se atoms are removed from the growth surface according to a thermally activated ESD process. Consequently, this effect is most pronounced at higher temperatures and at lower growth rates. While ESD is commonly observed for ionic compounds, its significance for MBE growth of II‐VI materials has not previously been discussed.

Optimal GaAs(100) substrate terminations for heteroepitaxy

The quality of heteroepitaxial growth of II‐VI materials on III‐V substrates, such as ZnSe on GaAs(100), depends strongly on the atomic structure and stoichiometry of the substrate. We define and describe those structures that optimize heteroepitaxial interface growth on GaAs(100) and related surfaces, and propose specific models for the c(6×4), ‘‘3×1’’, (4×6), an As‐lean version of the (2×4), and Se substitutional such as the (4×3). It is proposed that a good heteroepitaxial interface, with no extraneous fields and no charge imbalance, is achieved with substrate structures which lead directly to the appropriate interface stoichiometry.

‘‘Designer’’ interfaces in II‐VI/III‐V polar heteroepitaxy

The development of composite materials incorporating both II‐VI and III‐V compound semiconductors, such as ZnSe and GaAs, leads to the possibility of a variety of new devices of potential importance to the communications industry. In many cases, such as those involving resonant tunneling junctions and quantum well structures, the quality of the interface between the different compound semiconductors determines the ultimate quality of the device itself. Therefore, we have investigated the factors determining this interface quality for the GaAs/ZnSe system as prepared by molecular beam epitaxy. In this system, the stoichiometry of the substrate is of paramount importance. An excess of one constituent leads to high local electrical fields and poor interface morphology. Optimum growth of ZnSe on GaAs is achieved with GaAs substrate surfaces having a stoichiometry intermediate between the As‐ and Ga‐rich extremes. We will describe a model that defines the conditions for good interface formation and summarize e...

Organometallic molecular‐beam epitaxy growth and characterization of InxAl1−xAs on InP

We report the growth and characterization of InxAl1−xAs/InP heterostructures grown by organometallic molecular‐beam epitaxy. X‐ray rocking curves with half‐widths as low as 53 arc sec and low temperature photoluminescence linewidths of 26 meV were obtained for the InAlAs layers near lattice‐matched to InP. The interface quality was investigated by photoluminescence taking advantage of the type II nature of the interface. Interface quality was improved by reducing the length of the growth halt between layers. The important effects of interface chemistry were studied, and in fact, quality was enhanced by introducing binary interfacial layers only 1 ML in thickness.

Electrical characterization of gallium planar‐doped ZnSe grown by molecular‐beam epitaxy

We report electrical characterization of a series of ZnSe samples which are planar doped by a new approach to doping involving periodic deposition of sheets of Ga on Zn‐ or Se‐rich surfaces. For samples planar doped on Zn‐rich surfaces, the mobility could be described by ionized‐impurity scattering and polar optical‐phonon scattering mechanisms, while planar‐doped samples on Se‐rich surfaces and uniformly doped samples require additional scattering mechanisms to describe their mobilities. The latter two cases give higher mobilities than the first, a result which is in conflict with the fact that the latter have higher total ionized‐impurity concentrations and compensation. These results of higher mobilities along with higher total ionized‐impurity concentrations are interpreted as evidence of donor‐acceptor pair formation.

ZNSE/III–V Heterostructures Grown in a Multichamber MBE System

We have grown ZnSe epitaxial layers on bulk GaAs substrates and on GaAs epitaxial layers, with both As-rich and Ga-rich surface terminations. We have also grown ZnSe on AlAs epitaxial surfaces with different As to Al ratios. In all cases, abrupt, layer-by-layer growth is observed on the As-rich surfaces, while 3-dimensional nucleation is observed on the group III-rich surfaces. GaAs was also grown on ZnSe layers. In this case, microtwins form at the interface whose density diminishes as the layer is made thicker. A growth model is proposed consistent with these results which requires over-all electronic balance at the interface.