C. Lacelle

Structure property anisotropy in lattice-mismatched single heterostructures

Anisotropic optical, electrical, and structural properties have been observed in thick InxGa1−xAs/GaAs single heterostructures grown by low‐pressure metal‐organic vapor phase epitaxy on (001) and slightly misoriented GaAs substrates. The luminescence of the (001) samples is polarized and the electron mobility is higher along one of the 〈110〉 directions. Asymmetric distributions of surface ridges and misfit dislocations have been observed in secondary electron micrographs (SEMS) of the surfaces and in transmission electron micrographs. Strong anisotropy and a clear correlation between the anisotropic optical, electrical, and structural properties have been observed for samples grown on (001) oriented substrates. For (001) samples, the results indicate that the anisotropic properties are induced by nonuniform strain relaxation. For samples grown on misoriented substrates, SEM and micro‐Raman spectroscopy indicate a better crystal quality. The anisotropic properties are found to be reversed and the degree of...

Phonons in strained In1−xGaxAs/InP epilayers

Raman spectroscopy has been used to assess the concentration dependence of optical phonons in In1−xGaxAs epilayers grown by chemical beam epitaxy on InP(100). The alloy composition was varied from x=0.325 to x=0.55 to cover the technologically important and physically interesting range where the strain changes sign at x=0.468 from negative to positive. The Raman spectra were curve resolved to reveal the GaAs-like longitudinal optic (LO), disorder induced, InAs-like LO, and InAs-like transverse optic phonons. An examination of the concentration dependence of the phonon frequencies showed that the GaAs-like LO mode varied as ω(cm−1)=252.77+58.643x−50.108x2 for 0.325⩽x⩽0.55. A comparison of these results with previous infrared and Raman work on In1−xGaxAs has revealed that the concentration dependence of the optical phonon frequencies in the unstrained system is still not accurately known.

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.

Effects of substrate misorientation on anisotropic electron transport in InGaAs/GaAs heterostructures

The effects of substrate misorientation on anisotropic electrical properties of thick InGaAs layers grown on GaAs by low‐pressure metalorganic vapor phase epitaxy are studied. Hall bar samples oriented along [110] and [110] were cut from layers grown simultaneously on substrates oriented (a) exactly on (001) and (b) at 2° off (001) towards [011]. In layers grown on (001) oriented substrates a very large mobility anisotropy (μ[110]/μ[110]≊ 1000) is observed and attributed mainly to a lattice mismatch induced anisotropy. For the misoriented substrates, the average electron mobility increases by an order of magnitude and shows only a small residual anisotropy in the opposite direction (μ[110]/μ[110] ≊ 0.7).

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...

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.

Properties of InGaAs epitaxial layers lattice matched to InGaAs single crystal substrates

The structural and optical properties of InxGa1 − xAs (0 < x < 0.09) epitaxial layers grown by low pressure metalorganic vapour phase epitaxy (MOVPE) on lattice matched single crystal ternary alloy substrates with the same composition have been studied. They are compared with layers grown simultaneously on GaAs (lattice mismatch up to 0.06%) and on ternary substrates. The lattice matched layers are characterized by a narrow photoluminescence and X-ray linewidth which reflects their excellent structural quality. As the indium concentration increases, the improvement of these properties over those of mismatched layers and of the substrates themselves emphasizes the importance of lattice matched epitaxial buffer layers for the control of strain and defect density in strained structure devices even at relatively small indium concentration.

Comparative study of laser- and ion implantation-induced quantum well intermixing in GaInAsP/InP microstructures

Laser-induced quantum well intermixing (laser-QWI) and ion implantation-induced quantum well intermixing (II-QWI) techniques have been studied to selectively modify the optical properties of GaInAsP/InP laser microstructures. Following the annealing with a cw Nd:YAG laser, a blue shift in the quantum well photoluminescence of up to 124 nm was observed for samples annealed up to 4 min. A comparison of the laser annealing results with those of II-QWI, which were obtained for the same GaInAsP/InP microstructure, indicates that laser- QWI yields material with comparable, or better optical properties. The one-step processing used in the laser-QWI approach makes it an attractive alternative in fabricating photonic integrated circuits at low cost.