A. P. Roth

Structural and optical characterization of monolayer interfaces in Ga0.47In0.53As/InP multiple quantum wells grown by chemical beam epitaxy

We have carried out a detailed structural and optical characterization of Ga0.47In0.53As/InP multiple quantum wells grown by chemical beam epitaxy using a well‐defined sequence of growth interruption times between successive layers. These growth interruption times result in the formation of interfacial layers which drastically alter the structural properties of Ga0.47In0.53As/InP multiple quantum wells. An analysis of double‐crystal x‐ray diffraction data reveals that exposure of InP to arsine for 2 s is sufficient to create approximately 3 monolayers of InAs0.55P0.45 ternary under biaxial compressive strain at the InP/Ga047In0.53As interface. Moreover, exposure of Ga0.47In0.53As to phosphine for 2 s results in the formation of approximately 2 monolayers of Ga0.48In0.52As0.21P0.79 quaternary under biaxial tensile strain at the Ga0.47In0.53As/InP interface. We find that long exposures to hydrides (over 5 s) rather than short ones give rise to interfacial layers with less compositional disorder and/or thick...

Thermally induced In/Ga interdiffusion in InxGa1−xAs/GaAs strained single quantum well grown by LPMOVPE

Abstract A strained single quantum well of GaAs/In x Ga 1− x Ga/GaAs ( x =0.23) has been grown by low pressure MOVPE on a (100) GaAs substrate at 625° C. Samples were annealed under AsH 3 /H 2 at different temperatures in the range 750 to 900° C. Since the quantum well thickness (∼80 A) is below the critical value for this lattice mismatched system, we assume that the InGaAs layer is commensurate with the GaAs substrate. We analyse the low temperature (2 K) photoluminescence of the electron to heavy hole transition in the quantum well of these samples to study the In/Ga interdiffusion at the InGaAs/GaAs interfaces. The position in energy of the photoluminescence peaks shift to higher energies when annealing. The shifts are quantitatively interpreted in terms of changes in the quantum well profile due to the In and Ga interdiffusion. We determined the interdiffusion coefficient at 850° C to be 3×10 −17 cm 2 /s, with an activation energy 2.07 eV. The values obtained for the In/Ga interdiffusion coefficient are larger than those published for the Al and Ga interdiffusion in AlGaAs/GaAs heterojunctions.

Alloy broadening in photoluminescence spectra of GaxIn1−xAsyP1−y lattice matched to InP

Low temperature photoluminescence measurements of GaxIn1−xAsyP1−y alloys nearly lattice matched to InP to study the line broadening of the observed band to band and near band gap transitions in these materials were performed. We find that the dominant broadening mechanism is alloy broadening that originates from the spatial fluctuations of the band gap energy due to random anion and cation distribution. A model that assumes that occupation of the group‐III sites by Ga and In atoms and of the group‐V sites by As and P atoms occurs randomly, is fitted to the photoluminescence spectra of our samples. This provides an excellent description of the experimental results.

Growth of quantum wire structures by selective area chemical beam epitaxy

Abstract Selective area growth on silicon dioxide masked gallium arsenide substrates by chemical beam epitaxy is used to fabricate inverted V-shaped mesas. Indium gallium arsenide quantum wells grown on top of these mesas form quantum wire structures. The faceted mesa sidewalls are described as a function of substrate temperature and V III ratio in terms of a simple geometric model. The photoluminescence spectra show that the wire structure peak is shifted to longer wavelength compared to unpatterned substrates, for all growth temperatures. This shift is explained by the migration of indium. For low temperature growth, a second peak due to sidewall quantum wells is observed.

Faceted GaInAs/InP nanostructures grown by selective area chemical beam epitaxy

InP was grown by chemical beam epitaxy in narrow windows of widths varying between 20 and 2 μm, oriented along the [011] or [011] directions opened in a SiO2 mask on an (001) InP substrate. Several facets appear along the sidewalls and on the edge of the mesas owing to different growth rates on different crystallographic planes. These can be understood as consequences of the migration of group III species from one crystallographic plane to another. We have studied the formation of such facets and their effects on the growth of GaInAs/InP structures of various thicknesses. The samples were studied using a field emission scanning electron microscope (SEM) and low temperature photoluminescence (PL). SEM micrographs show that for lines oriented along the [011] direction the dominant InP sidewall facets are (111)B planes on which GaInAs does not grow as long as Ga and In species can migrate towards (001). For the orthogonal direction, however, the lateral growth rate of the InP sidewalls is large and the face...

A PHOTOMODULATED SPECTROSCOPY STUDY OF INXGA1-XAS/GAAS SUPERLATTICES AND QUANTUM WELLS

We present here a detailed study of photomodulated transmission and reflectivity at room and liquid‐nitrogen temperatures of a series of In x Ga1−x As/GaAs superlattices and a single quantum well. Our samples span a variety of alloy compositions and quantum‐well widths. We compare the results of our measurements with the predictions of an envelope‐function calculation, which includes wave‐vector dependence of the minibands. This comparison allows identification of several spectral features unmistakably arising from miniband dispersion. Also, accurate determination is made of the band‐offset parameter, whose value is discussed in the context of those obtained by other authors.

Anisotropic Transport in InGaAs/GaAs Heterostructures Grown by Movpe

Anisotropic electron transport has been observed in In x Ga 1-x As/GaAs heterostructures grown by MOVPE on (001) and intentionally misoriented GaAs substrates. The low field electron mobilities in two perpendicular directions are found to be higher in the [110] direction than in the [ 1 10] direction. The ratio of µ [110] /µ [ 1 10] derived from Hall measurements is related to the degree of substrate misorientation as well as epilayer composition. Finally, the photoluminescence spectra are polarized along orthogonal directions. These anisotropic properties are directly related to the anisotropy of [110] and [ 1 10] dislocations due to lattice mismatch between the substrates and the layers.

Electrical, optical properties, and surface morphology of high purity InP grown by chemical beam epitaxy

High purity InP layers have been grown by chemical beam epitaxy using H2 as the carrier gas for transporting the metal alkyl trimethylindium into the growth chamber. InP layers exhibiting Hall mobility as high as 238 000 cm2/V s at 77 K and with a peak value of 311 000 cm2/V s at 50 K and residual Hall concentration of 6×1013 cm−3 at 77 K were grown at 500 °C using a low V/III ratio (2.2) and a phosphine (PH3) cracking cell temperature of 950 °C. The 4.2 K photoluminescence spectra were dominated by donor bound exciton (D0,X)n up to n=6 and free exciton (X) transitions for InP layers grown above 500 °C. All the InP samples exhibited very weak acceptor related photoluminescence transitions indicating very low concentration of acceptors. The energy of these transitions suggests that Mg is the major residual acceptor. Donor impurity identification by high resolution magnetophotoluminescence indicated that S and Si are the major impurities. PH3 has been found to be the major source of S impurities in the pres...

Structure damage in reactive‐ion and laser etched InP/GalnAs microstructures

Etching of a chemical‐beam‐epitaxy‐grown InP/InGaAs multilayer structure with reactive ion etching (RIE) and laser‐assisted dry etching ablation (LADEA) is carried out in order to evaluate the extent of the damage induced by these two etching methods. Micro‐Raman spectroscopy indicates a systematic broadening of the phonon lines as a function of depth of a RIE fabricated crater. In contrast, LADEA which is based on the application of an excimer laser for the removal of the products of chemical reaction, shows no measurable changes in the phonon line widths when compared to as‐grown material. The results suggest that LADEA has potential for the photoresistless fabrication of damage free microstructures.

Structural and optical characterization of InP/GaxIn1−xAsyP1−y quantum wells and interfacial layers

Several multiquantum wells of InP/Ga x In1−x As y P1−y grown by chemical‐beam epitaxy have been studied by high‐resolution x‐ray diffraction, low‐temperature photoluminescence, and Raman scattering to characterize interfacial layers between the barriers and the wells. These interfacial layers are created during the initial stage of growth of the quaternary material as a result of the longer transient for the saturation of the group‐III elements flux. The combination of x‐ray diffraction and photoluminescence allows a precise determination of the interfacial layer thickness and composition grading and shows that interface roughness is of the order of 1 monolayer.Raman scattering confirms these results and is used to determine values of the sound velocity and of the index of refraction in the quaternary alloy material.