Precipitation Phenomena Associated with Ultra-High Be Doping in Ga 0.47 In 0.53 P Layers grown by MBE
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PRECIPITATION PHENOMENA ASSOCIATED WITH ULTRA-HIGH Be DOPING IN GaoA47 Ino.53 P LAYERS GROWN BY MBE C.M. COTELL, M.B. PANISH, R.A. HAMM, L.C. HOPKINS, AND J.M. GIBSON AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 07974 ABSTRACT Ultra-high Be doping of Gao.47 In 0.53 As layers grown by gas source molecular beam epitaxy has shown that for each growth temperature, there exists a maximum hole concentration (>_lxl&0 °cm-3 ). Increasing the Be flux above that which produces the maximum hole concentration results in a degradation of the crystalline quality of the films. The degradation of film quality results from precipitation of a Be-rich phase on the surface during growth and nucleation of dislocations at each precipitate. Below that concentration, some of the Be segregates and floats on the growing surface. INTRODUCTION Ultra-high Be doping of Ga0.4 7 In0.53 As by low temperature molecular beam epitaxy has recently been reported.[1l] Carrier concentrations, NA-ND, as high as 5.6x10 °cm-3, as determined by room temperature Hall measurements, were achieved at a growth temperature of 365°C. The effect of growth temperature on the maximum doping level has been characterized. For each temperature, a value for NA-ND is reached for which a further increase in Be flux results in an abrupt deviation of NA-ND below that expected from the temperature dependence of the vapor pressure of Be. It has been suggested [1] that some precipitation-related phenomenon may explain the abrupt drop in carrier concentration with Be flux at high doping levels. In this paper, we report the results of characterization of highly-Be-doped samples by transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). EXPERIMENTAL All of the samples for this study were grown by hydride source molecular beam epitaxy (HSMBE). [2,3] In this version of gas source MBE, decomposed AsH 3 and PH 3 were used for the generation of As 2 and P2 beams, and effusion cells containing the elements were used to generate atomic beams of Ga, In, and Be. [2,3] The growth on semi-insulating substrates and substrate temperature monitoring procedures are described in ref. [1]. The growth rate for the ternary was 1.2 rim/hr and layer thicknesses ranged from 500 to 4000 A. The range of growth temperatures studied was 365°C to 505 0 C. The microstructures of the samples were characterized in planar- and cross-section using a Philips 430 transmission electron microscope operating at 300 kV. The chemical composition of the samples was studied with secondary ion mass spectrometry (SIMS) using a Cameca IMS-3F instrument operating at 8 keV with an 02+ primary beam. The raster area was 250x250 Jim 2 and secondary ions were extracted from a 60 Jim-diameter region at the center of the crater. The Be+ signal was monitored and referenced to the As+ signal. The vertical scale was calibrated with a sot~otndard sample of Be-implanted GalnAs. The horizontal scale was based on a sputter rate of 3-5 A/s for GaInAs, as determined by profilometer measurements of
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