C. Lavoie

Semiconductor substrate temperature measurement by diffuse reflectance spectroscopy in molecular beam epitaxy

The temperature of semiconductor substrates used in molecular beam epitaxy is determined from the diffuse reflection spectrum (DRS) of the substrates, measured with an external light source. The relative sensitivity of the technique is better than 1 °C. The absolute calibration of the DRS technique for substrates of different thickness, conductivity and back surface texture, is described. The DRS technique is also sensitive to changes in front surface roughness as demonstrated by the increase in the diffuse reflectance at short wavelengths when the oxide desorbs.

Semiconductor substrate cleaning and surface morphology in molecular beam epitaxy

Abstract In-situ laser light scattering shows that the surface morphology of GaAs substrates during the initial stages of homoepitaxial growth is a sensitive indicator of substrate cleanliness. Oxide removal by atomic-hydrogen etching has no effect on the morphology of polished (100) GaAs substrates, while thermal oxide desorption roughens the surface. Carbon contamination of the surface causes roughening during subsequent film growth. Secondary ion mass spectrometry and photoemission spectroscopy show that atomichydrogen etching reduces the carbon contamination on the substrate but does not remove silicon oxide. Synchrotron radiation photoemission measurements show that some as-received substrates are contaminated with a thin uniform layer of SiO 2 .

Factors affecting the temperature uniformity of semiconductor substrates in molecular‐beam epitaxy

The temperature of GaAs substrates is profiled in a molecular‐beam epitaxy system with a spatial resolution of 3 mm and a thermal resolution of 0.4 °C, respectively. The effects of substrate doping, back surface textures, thermal contact to the holder, and a pyrolytic boron nitride diffuser plate, on the temperature uniformity, are explored for indium‐free mounted substrates. Both positive and negative curvature temperature profiles are observed.

Cross‐sectional imaging of doped layers in epitaxial gallium arsenide films by scanning tunneling microscopy

Cross sections of epitaxial GaAs/GaAlAs layers have been imaged by scanning tunneling microscopy in air, and individual doped layers with different conductivity type have been resolved for the first time in air. In constant current images acquired with a positive tip bias, the n regions appear to be higher than the p regions, by ∼5 A depending on the junction bias due to an electronic contrast mechanism. A new imaging method is described which decouples the electronic contrast from the topography. In this method, one obtains an image by repetitively interrupting the feedback loop and sampling the tunneling current at a different tip–sample voltage, selected to yield high conductivity‐type contrast.

Effect of growth conditions on surface roughening of relaxed InGaAs on GaAs

We report elastic light scattering measurements of the surface morphology of strained InxGa1–xAs on GaAs, grown by molecular beam epitaxy at different growth temperatures and In contents. During strain relaxation through formation of interfacial misfit dislocations, the surface of the film roughens in response to inhomogeneous surface strains produced by the interfacial misfit dislocations. The time dependence of this roughening is modeled by an Edwards–Wilkinson equation in which the deposition flux noise is neglected and the inhomogeneous surface stress is the only driving term.

Light Scattering Study of the Evolution of the Surface Morphology During Growth of Ingaas on GaAs

In-situ elastic light scattering is used to measure the evolution of the surface morphology of In{sub x}Ga{sub 1{minus}x}As films during molecular beam epitaxy growth on GaAs substrates. The in-situ measurements are compared with ex-situ measurements o the surface morphology on quenched films by optical scatterometry and atomic force microscopy (AFM). The AFM results are in good agreement with the rms roughness obtained from light scattering and both techniques detect the onset of misfit dislocation formation in this system.