R. M. Park

p‐type ZnSe by nitrogen atom beam doping during molecular beam epitaxial growth

A novel approach to producing p‐type ZnSe epitaxial layers is reported which involves nitrogen atom beam doping during molecular beam epitaxial growth. Net acceptor concentrations as large as 3.4×1017 cm−3 have been measured in nitrogen atom beam doped ZnSe/GaAs heteroepitaxial layers which represents the highest acceptor concentration reported to date for ZnSe:N epitaxial material grown by molecular beam epitaxy. In addition, light‐emitting diodes based on ZnSe:N/ZnSe:Cl, p‐n homojunctions have been found to exhibit dominant electroluminescence in the blue region of the visible spectrum at room temperature.

Growth of zinc blende‐GaN on β‐SiC coated (001) Si by molecular beam epitaxy using a radio frequency plasma discharge, nitrogen free‐radical source

We report the growth of zinc blende‐GaN epitaxial films on β‐SiC coated (001) Si substrates using a molecular beam epitaxy approach in which the reactive nitrogen species are generated in a remote 13.56 MHz rf plasma discharge, nitrogen free‐radical source. We postulate, based on optical emission spectroscopy studies of the remote plasma, that, in our study, nitrogen atoms are the species primarily responsible for efficient nitridation. The zinc blende nature of the GaN films was confirmed by in situ reflection high‐energy electron diffraction, ex situ x‐ray diffraction, and ex situ low‐temperature photoluminescence analyses. Our zinc blende‐GaN film growth rates (∼0.3 μm/h) are higher than those reported to date that involve the use of electron cyclotron resonance type reactive nitrogen sources.

Blue‐Green Diode Lasers

The development of compact, reliable and inexpensive short‐wavelength lasers is certain to have profound effects on virtually any technology that uses coherent visible light. Although the impact of such devices will be far‐reaching, the primary driving force behind efforts to develop blue‐green diode lasers is without question optical recording. The demand for increased data storage capabilities is continually forcing the recording industry to increase storage densities.The development of compact, reliable and inexpensive short‐wavelength lasers is certain to have profound effects on virtually any technology that uses coherent visible light. Although the impact of such devices will be far‐reaching, the primary driving force behind efforts to develop blue‐green diode lasers is without question optical recording. The demand for increased data storage capabilities is continually forcing the recording industry to increase storage densities.

Growth by molecular beam epitaxy and electrical characterization of Si‐doped zinc blende GaN films deposited on β‐SiC coated (001) Si substrates

We report the electrical characteristics of heavily Si‐doped zinc blende GaN epilayers deposited on β‐SiC coated (001) Si substrates. The β‐GaN films were grown by molecular beam epitaxy using a rf plasma discharge, nitrogen free‐radical source, and the doping concentration in the films was controlled over the range 1.5×1018–3.0×1020 cm−3 by suitably adjusting the temperature of a Si effusion cell. We have found that Si incorporation in β‐GaN results in a relatively deep donor level (∼62 meV below the conduction band edge at a carrier concentration at room temperature of 1018 cm−3). Also, we present evidence of simultaneous high mobility conduction band conduction (dominant at high temperatures) and low mobility impurity band conduction (dominant at temperatures <70 K) in heavily doped (nRT≳1019 cm−3) material.

GaAs substrate cleaning for epitaxy using a remotely generated atomic hydrogen beam

In situ GaAs surface cleaning prior to molecular beam epitaxy using a combined thermal/H‐atom treatment, the H‐atom flux being derived from a rf (13.56 MHz) plasma discharge, hydrogen free‐radical source, has been compared and contrasted to conventional thermal treatment of GaAs surfaces. Surface quality, i.e, morphology, was monitored in situ in real time using conventional reflection high‐energy electron diffraction and a diffuse optical reflectivity technique employed simultaneously. GaAs surfaces were found to clean readily at temperatures below 400 °C using the combined thermal/H‐atom treatment as opposed to the conventional thermal treatment, which requires temperatures in the vicinity of 600 °C. The atomically clean GaAs surfaces were also found to be specular when prepared using the combined thermal/H‐ atom treatment in contrast to conventional thermally treated GaAs surfaces, which are considerably rough on the atomic scale, surface roughening in the conventional case being associated with the ox...

Strain relief study concerning the InxGa1−xAs/GaAs (0.07<x<0.5) material system

The evolution of dislocations in the InxGa1−xAs/GaAs material system has been studied as a function of the ternary alloy comparison in the range 0.07<x<0.5. Cross‐sectional transmission electron microscope observations indicate that for x<0.18, threading dislocations are absent in the epilayer and dislocations propagate from the heterointerface into the GaAs material, while, for 0.18<x<0.28, dislocations appear to propagate into both the epilayer and the GaAs. Furthermore, for x ≳0.28, all the dislocations are observed in the epilayer while the GaAs appears to be dislocation‐free. We propose a model involving the balance of forces acting on misfit dislocations generated at the heterointerface which includes a surface image force term to explain our observations of dislocation evolution as a function of the ternary alloy composition.

Application of ‘‘critical compositional difference’’ concept to the growth of low dislocation density (<104/cm2) InxGa1−xAs (x≤0.5) on GaAs

Multilayer epitaxial structures consisting of InxGa1−xAs layers of various compositions were grown on GaAs substrates by the molecular beam epitaxy technique. Dislocation evolution and residual strain in these heterostructures were studied using cross‐sectional transmission electron microscopy (XTEM) and high‐resolution x‐ray diffraction analyses, respectively. The multilayer heterostructures were designed such that the compositional difference between two adjacent InxGa1−xAs layers in the stack was less than a critical compositional difference of Δx=0.18, taking partial lattice‐relaxation into account. XTEM studies of the stacked structures indicated dislocation evolution to be confined to the GaAs substrate and the InxGa1−xAs layers underlying the top InxGa1−xAs layer in the stack, the top InxGa1−xAs layer being essentially dislocation‐free. This phenomenon is attributed to a monotonic increase in the yield strength of InxGa1−xAs at the appropriate growth temperatures with increasing values of x. Such b...

Residual strain analysis of InxGa1- xAs/GaAs heteroepitaxial layers

InxGa1−xAs/GaAs heteroepitaxial layers, having various compositions and thicknesses, have been analyzed using the high resolution x‐ray diffraction technique which has revealed that the residual strain in the epilayers is strongly dependent on both the epilayer composition as well as thickness. However, published theoretical models concerning residual strain in InxGa1−xAs/GaAs epilayers suggest that the extent of relaxation is independent of epilayer composition. In this letter, we present an empirical model based on our findings which can be used to accurately predict the extent of lattice relaxation in InxGa1−xAs/GaAs epilayers which includes the influence of epilayer composition.

On the kinetics of growth of highly defective GaN epilayers and the origin of the deep trap responsible for yellow-band luminescence

The kinetics of growth of GaN/(0001) sapphire heteroepitaxial films have been examined in the relatively low substrate temperature range, 560–640 °C, using the reflection high energy electron diffraction (RHEED) specular reflection intensity monitoring technique. In particular, an alternate element exposure method of growth was employed in which Ga and N atoms were supplied separately (rather than simultaneously, as in conventional molecular beam epitaxy) to the substrate with the inclusion of a time delay between successive Ga flux and N flux exposures. We interpret the observed time dependent recovery of the RHEED specular reflection intensity during the time delay phases to be associated with Ga–N surface molecule migration on Ga-terminated surfaces and the activation energy for this migration process was determined to be 1.45±0.25 eV.

Modified donor–acceptor pair luminescence in heavily nitrogen‐doped zinc selenide

The luminescence from heavily doped ZnSe:N shows a deep broadband whose position was found to depend strongly on the excitation intensity and sample temperature. The peak was found to shift towards higher energies with increasing intensity, but in contrast to the standard donor–acceptor pair (DAP) model, shifted towards lower energies with increasing temperatures. This behavior is explained using a modified DAP model that takes into account the perturbations of the band and impurity states caused by fluctuations in the concentrations of the ionized impurities. This model led to an estimate of 2.52 eV for the PL peak, with a width of 140 meV, for the case of low temperature and low excitation intensity, in rough agreement with our observations. The effect of these fluctuations on film conductivity is also discussed.