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By thermally evaporating CaF2 and NdF3, we have grown Nd-doped CaF2 films on Si(111), A1/Si(111) and quarter-wavelength Ta2O5/SiO2 multilayer Bragg reflectors. The optical and structural properties of the CaF2:Nd films are characterized by photoluminescence spectroscopy (PL) and x-ray diffraction. The effects of different Nd concentration, growth temperatures and post-annealing were studied. Regardless of the substrates, the as-grown films show emission lines at wavelengths similar to bulk CaF2:Nd. Annealing the films at 700°C in forming gas results in a new emission pattern. Little difference between the PL spectra of polycrystalline and single crystal CaF2:Nd films is observed, indicating that the luminescence efficiency is insensitive to the crystalline quality of the films.
In this paper, the effect of atomic hydrogen on carbon impurity incorporation during the metalorganic-molecular-beam-epitaxy (MOMBE) growth of GaAs is studied. Atomic hydrogen was introduced into the MOMBE chamber during the growth by cracking molecular hydrogen with a high temperature cracker cell. Atomic hydrogen appears to be effective in reducing the background doping level of MOMBE-grown GaAs, presumably by reacting with hydrocarbon radicals. Background doping levels as low as 4 × 1014 cm−3 and room temperature hole mobilities as high as 430 cm2/V-sec were achieved. This result demonstrates that it is feasible to grow high quality GaAs films in MOMBE without using AsH3 or a high flux of As4by introducing atomic hydrogen into the chamber during the growth.
Results from high resolution helium temperature photoluminescence (PL) spectroscopy have been correlated to precision lattice constant and transport measurements and to theoretical band gap versus composition behavior. It is found that low temperature PL spectra provide precise determination (+/- 0.02%) of ZnTe mole fraction as well as carrier type, relative impurity concentration and point defect properties of these substrates. In addition helium and room temperature PL results are correlated to determine the accuracy of room temperature measurements for composition determination.
A two step rapid thermal anneal (RTA) has been studied for activating Be implanted GaAs, where a short duration, high temperature step is used to electrically activate the Be followed by a longer, low temperature anneal for lattice regrowth. p-n diodes show a substantial reduction in reverse diode leakage current after the low temperature second step anneal, when compared to a single step RTA or to furnace annealing (FA). For low energy Be implants, no difference in elecrical activiation between the two step anneal is observed. Raman studies demonstrate that residual substrate impurities and high Be concentrations inhibit restoration of single crystal lattice characteristics after RTA. Lattice quality is shown not to limit diode characteristics in the RTA material.
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