G. W. Wicks

Magnesium‐ and calcium‐doping behavior in molecular‐beam epitaxial III‐V compounds

Residence lifetimes of Mg on GaAs surfaces were observed using 10 KV reflection electron diffraction and Auger electron spectroscopy to decrease from ∼120 s at 550 °C to ∼1 s at 600 °C. The electrical incorporation coefficient is ∼0.3 at and below 500 °C decreasing to ∼3×10−4 at 600 °C at the expense of desorption. Hole mobilities of uniformly Mg‐doped samples are as good as those for equivalently Be‐doped GaAs samples. Calcium does not behave as a shallow acceptor in GaAs grown by molecular‐beam epitaxy.

Anomalous redistribution of beryllium in GaAs grown by molecular beam epitaxy

The purpose of this study is to investigate anomalous redistribution of beryllium (Be) in GaAs grown by molecular beam epitaxy (MBE). A concentration‐dependent diffusion coefficient for Be is found from the substitutional‐interstitial diffusion model. The importance of the generation of BeI from Ga point defects (vacancies or interstitials) in the diffusion process is also presented. Extremely rapid interstitial diffusion during growth, on the order of 30 μm in 1 h at 680 °C, has also been observed. This effect begins to occur for hole concentrations above 1019/cm3. Unintentional incorporation of Be into GaAs grown after closing the Be shutter is also presented. Consideration of the surface concentration of Be during MBE growth facilitates the explanation of this memory effect.

Calculation of the conduction band discontinuity for Ga0.47In0.53As/Al0.48In0.52As heterojunction

Photoluminescence studies at 4 K on Ga0.47In0.53As/ Al0.48In0.52As single quantum wells exhibit emission ranging from 1.318 eV for a 15‐A well to 0.82 eV for thick wells. The emission energy of each single quantum well is compared to theoretical curves which are generated from a finite potential square well model. The closest agreement between the experimental curves and the theoretical curves occurs when the conduction band discontinuity is taken to be 70% of the band‐gap discontinuity or 0.52 eV.

GaInAs‐AlInAs structures grown by molecular beam epitaxy

Growth of GaInAs and A1InAs by molecular beam epitaxy on idium phosphide substrates is reported. Unintentionally doped, closely lattice matched GaInAs layers were n‐type with μ300 up to 8800 cm2 V−1 s−1 and n as low as 1×1016 cm−3 whereas undoped A1InAs layers were typically high resistance. 2‐MeV Rutherford backscattering showed good GaInAs crystal quality although the A1InAs was somewhat disordered. Evidence for cation exchange at interfaces and surface accumulation of indium was evident from both RBS and sputter Auger profiles. In situ grown A1 films on A1InAs showed an effective barrier height∼0.8 eV from 1/C2 V s V curves, however attention to the forward I‐V characteristics indicated lower values. DLTS results indicate the GaInAs to be virtually trap‐free but that A1InAs has high deep level concentrations owing to low growth temperatures. Good photoluminescent efficiencies were demonstrated for GaInAs layers, however, poor results were obtained for A1InAs.

Defect structure and intermixing of ion-implanted AlxGa1−xAs/GaAs superlattices

Cross‐sectional transmission electron microscopy and Raman spectroscopy have been used to study the defect structure and intermixing of annealed ion‐implanted Al0.3Ga0.7As/GaAs superlattices. The results show clearly that the amount and depth of superlattice layer intermixing depends on the ion mass. In superlattices that retain their structure after implantation and annealing, the distribution of defect clusters (primarily interstitial loops) is inhomogeneous; most defect clusters are nucleated in the GaAs layers. Examination of unannealed superlattice samples reveals that ion beam damage occurs preferentially in the GaAs layers.

Luminescence line shape broadening mechanisms in GaInAs/AlInAs quantum wells

GaInAs/AlInAs single quantum wells have been grown lattice matched to InP substrates by molecular beam epitaxy. The quantum well thicknesses ranged from 15 to more than 100 A. The low‐temperature photoluminescence exhibited a monotonically increasing spectral linewidth with decreasing well thickness. Of the several possible broadening mechanisms of the quantum well photoluminescence, two mechanisms were found to dominate: one mechanism for thin wells and one for thick wells. Quantum wells thicker than 50 A were found to have their low‐temperature photoluminescence spectra broadened primarily by a transfer of electrons from the AlInAs cladding layers into the GaInAs quantum well. Wells thinner than 50 A had their photoluminescence broadened mainly by interface roughness.

Optical properties of AlxIn1−xP grown by organometallic vapor phase epitaxy

AlxIn1−xP epilayers grown by organometallic vapor phase epitaxy are characterized by electroreflectance, photoluminescence, and Raman spectroscopy. Electroreflectance measurements of the E0 band gap show significant bowing of the direct band gap with composition. The compositional dependence of the direct gap is found to be EΓ(x)=1.35+1.83x+0.38x2 (eV). In the Raman scattering spectrum, the AlP‐like longitudinal optical phonon mode is identified and its energy is measured as a function of composition.

Improvement of optical characteristics of Al0.48In0.52As grown by molecular beam epitaxy

The photoluminescence linewidth (4 K) of Al0.48In0.52As was reduced to 15 meV and its dependence was determined to be a strong function of the substrate temperature and As4 overpressure. Raman spectroscopy correlates the luminescence broadening to the crystallinity of the AlInAs. The ratio of the allowed longitudinal optical phonon to forbidden transverse optical phonon Raman peak heights is 10:1.

Properties of AlxGa1−xAs (xAl≂0.3) grown by molecular‐beam epitaxy on misoriented substrates

The effects of substrate misorientation on the morphological and optical properties of AlxGa1−xAs (xAl≂0.3) grown by molecular‐beam epitaxy (MBE) have been studied. The substrate temperatures and V/III beam‐flux ratios used were such that layers grown on nominally (100) substrates typically exhibited rough morphologies and poor 4.2 K PL characteristics. By intentionally misorienting the substrate slightly from (100), smooth layers can be grown at 620 and 650 °C at typical MBE growth rates (≂1 μm/h). These smooth layers also exhibited sharp, exciton‐related emission peaks at 4.2 K with half‐widths as narrow as 5 meV. Since rough surfaces may lead to poor interfaces between GaAs and (Al,Ga)As and in turn to degraded performance in heterojunction devices, the present results may have significant implications for the performance of such structures grown by MBE.

Reflection high‐energy electron diffraction intensity oscillation study of Ga desorption from molecular beam epitaxially grown AlxGa1−xAs

Reflection high‐energy electron diffraction (RHEED) intensity oscillations are used as an in situ probe to study Ga desorption during molecular beam epitaxial growth of AlxGa1−xAs. A simple thermodynamic model is developed which, in the limit of low As4 : group III beam flux ratios, accurately predicts the measured changes in AlxGa1−xAs growth rate and composition due to Ga desorption at elevated growth temperatures. The desorbing Ga flux is observed to be less in thin epitaxial layers of GaAs growing on top of AlGaAs than in bulk GaAs, giving rise to a growth rate transient at heterointerfaces.