GaN x As 1−x layers with different nitrogen concentrations x grown on (001)GaAs substrates by molecular-beam epitaxy have been studied by photoluminescence, optical absorption, and Raman spectroscopy. The content of nitrogen in the layers was determined by x-ray diffraction and secondary-ion-mass spectrometry. The samples can be classified in three categories with respect to the concentration of N: with doping nitrogen concentration, with average content of N less than 0.3, and with x close to 1. From optical measurements and from analysis of x-ray diffraction spectra, different phases are observed in the GaNxAs1−x layers: GaAs, GaN, and the solid ternary solution GaNxAs1−x. In Raman spectra both GaAs-like and GaN-like optical phonons are observed. We have estimated the fundamental band-gap energy in the GaNxAs1−x alloy with low nitrogen concentration up to x=0.04 from absorption measurements, and in GaNxAs1−x with high nitrogen concentration x>0.96 from photoluminescence spectra. Fitting of the experimental data for low x values gives a constant bowing parameter as big as b=−18 eV. This value predicts the band-gap energy for the high nitrogen concentration in agreement with experimental data. Consequently, GaNxAs1−x is predicted to be semimetallic in the range 0.12<x<0.75.

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It is demonstrated that it is possible to investigate details of the electronic structure of an internal atomic monolayer using soft-x-ray-emission spectroscopy. The local and partial density of states of one monolayer and three monolayers of Si, embedded deep below a GaAs(001) surface, was extracted. Clear differences to the density of states for bulk Si were observed.Original Publication:P. O. Nilsson, J. Kanski, J. V. Thordson, T. G. Andersson, J. Nordgren, J. Guo and Martin Magnuson, Electronic structure of buried Si layers in GaAs(001) as studied by soft-x-ray emission, 1995, Physical Review B. Condensed Matter and Materials Physics, (52), R8643-R8645.http://dx.doi.org/10.1103/PhysRevB.52.R8643Copyright: American Physical Societyhttp://www.aps.org

An A1036Gao 64As/Al Ga& As inverse parabolic quantum-well structure was grown by molecularbeam epitaxy using both digital and analog compositional grading techniques. Photoluminescence and photocurrent measurements showed distinct exciton peaks for both types of wells. A large Stark shift was found for the digital well, in agreement with the calculations. An observed deviation for the analog well was ascribed to Auctuation in quantum-well parameters. Finally, advantages and disadvantages of the two growth techniques are discussed.

The initial molecular beam epitaxy growth of GaN on GaAs(001) was studied by real-time monitoring of the (3×3) surface reconstruction and its transition to an unreconstructed (1×1). Various growth conditions were established by variation of the V/III ratio, i.e., the Ga flux. We characterized the effect of the first two strained GaN monolayers: a N-terminated GaN (3×3) monolayer and a second unreconstructed (1×1) monolayer. A series of samples were grown under N-rich, Ga-rich, and near-stoichiometric growth conditions. The resulting morphology of the interface region was analyzed by high-resolution scanning electron microscopy, Auger-electron spectroscopy, and double crystal x-ray diffractometry. The N-rich and Ga-rich conditions resulted in extensive defect formation due to the nitridation damage of the GaAs substrate. The extent of this was found to be determined by the properties of the first GaN monolayer. The surface roughness under optimum growth conditions could be as low as ∼20 nm, defined by nanocrystalline grains, showing no observable nitridation damage.