Kinetic modeling of microscopic processes during electron cyclotron resonance microwave plasma-assisted molecular beam epitaxial growth of GaN/GaAs-based heterostructures

Abstract

Microscopic growth processes associated with GaN/GaAs molecular beam epitaxy ͑MBE͒ are examined through the introduction of a first-order kinetic model. The model is applied to the electron cyclotron resonance microwave plasma-assisted MBE ͑ECR-MBE͒ growth of a set of ␦-GaN y As 1Ϫy /GaAs strained-layer superlattices that consist of nitrided GaAs monolayers separated by GaAs spacers, and that exhibit a strong decrease of y with increasing T over the range 540-580°C. This y͑T͒ dependence is quantitatively explained in terms of microscopic anion exchange, and thermally activated N surface-desorption and surface-segregation processes. N surface segregation is found to be significant during GaAs overgrowth of GaN y As 1Ϫy layers at typical GaN ECR-MBE growth temperatures, with an estimated activation energy E s ϳ0.9 eV. The observed y͑T͒ dependence is shown to result from a combination of N surface segregation/desorption processes. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01211-3͔The wide band-gap refractory semiconductor, GaN, related alloys, and heterostructures have recently come under active investigation due to their technological promise as light emitters in the blue to UV region.1-3 While much recent GaN research has emphasized growth of device structures ͑blue LEDs and lasers͒ on various substrates, 4 -6 comparatively little work has concentrated on the microscopic growth processes that are of significance, for example, in the electron cyclotron resonance plasma-assisted molecular beam epitaxial ͑ECR-MBE͒ growth of GaN-related heterostructures. Recently, we have shown 7,8 that it is possible to produce high quality, fully commensurate GaN y As 1Ϫy /GaAs strained-layer superlattices ͑SLS͒. Analysis of such structures through time-resolved reflection high energy electron diffraction ͑RHEED͒ and high-resolution x-ray diffraction ͑HRXRD͒ measurements recently revealed evidence of distinct thermally activated microscopic processes, but, in the absence of a quantitative model to consistently account for these separate RHEED and HRXRD observations, only tentative identification of processes, and at best, semiquantitative assessment of kinetics has been possible to date. 8In this letter, we examine the initial nitridation, N surface desorption, and N surface segregation processes observed in ECR-MBE-grown GaN y As 1Ϫy /GaAs heterostructures through the introduction of a quantitative model that is based on first-order kinetic theory. For the first time, the existence of a thermally activated N surface-segregation mechanism, which appears to be significant under typical GaN/GaAs ECR-MBE growth conditions, is conclusively established and quantitatively assessed. Through application of our model to an unusually strong growth temperature dependence of y in GaN y As 1Ϫy /GaAs superlattices, the existence of a strong N-surface-segregation mechanism, which we suggested previously, 8 but could not conclusively establish in the absence of a suitable quantitative model ͑which is necessary to adequately describe the...

Atomic-scale structure and electronic properties of GaN/GaAs superlattices

“…The fraction of black regions is 4.45  0.05  10 -3 , which corresponds to only about (1/5) monolayer of GaN per deposited layer, rather than the full monolayer assumed earlier. 8 A similar fractional area of clusters is obtained in several large-scale images, with total area > 0.2 m 2 . High resolution x-ray diffraction data of these GaN/GaAs superlattices indicates an average superlattice lattice constant, 5.6499 Å, previously interpreted in terms of (continuous) monolayers of GaAs 0.79 N 0.21 embedded in 192 Å GaAs layers.…”

“…High resolution x-ray diffraction data of these GaN/GaAs superlattices indicates an average superlattice lattice constant, 5.6499 Å, previously interpreted in terms of (continuous) monolayers of GaAs 0.79 N 0.21 embedded in 192 Å GaAs layers. 8 With the knowledge of the fractional area of the clusters, we estimate a cluster lattice constant of 4.6  0.1 Å, similar to bulk GaN. Therefore, we conclude that the nitrided regions consist of pure GaN, as opposed to some alloy composition with 20%  30% N.…”

Atomic-scale nature of the (3×3)-ordered GaAs(001):N surface prepared by plasma-assisted molecular-beam epitaxy

“…[11][12][13] While a rough and relaxed surface morphology is typically found after a prolonged exposure of active nitrogen in most of nitridation studies reported to date, 10,11 Hauenstein et al 11 have recently shown by using reflection high-energy electron diffraction ͑RHEED͒ results that a specular, (3ϫ3)-ordered, and coherently strained GaN film ͑approximately one monolayer in thickness͒ can be formed on GaAs͑001͒ through limitedexposure surface nitridation. 9,10 Despite its importance for growing nitride materials and Ga(As 1Ϫx N x ) mixedanion alloys, very little has been known about the atomicscale nature of the nitridation process.…”

Nanometer-scale studies of nitride/arsenide heterostructures produced by nitrogen plasma exposure of GaAs

“…Apparently, thick layers (>0.5 µm) of dilute GaAs 1-x N x (x ≤ 0.03) alloys have been produced by nitride growth, 4,5 and attempts to increase the nitrogen composition in the alloy using GaAs surface nitridation resulted in GaAs/GaN/GaAs thin-layer structures 6 and δ-GaAs 1-x N x /GaAs superlattices (0.04 ≤ × ≤0.33). 7,8 The identification of the nitride/arsenide structures as binary or ternary alloys has relied upon x-ray diffraction (XRD), which has spatial resolution of hundreds of µm and averages over many surface layers parallel to the interfaces. Similarly, cross-sectional transmission electron microscopy (XTEM) images may represent an average over many surface layers perpendicular to the interfaces of interest.…”