Relaxed InAsP layers grown on step graded InAsP buffers by solid source MBE
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Relaxed InAsP layers grown on step graded InAsP buffers by solid source MBE M. K. Hudait1, Y. Lin1, C. L. Andre1, P. M. Sinha1, C. A. Tivarus2, J. P. Pelz2, D. M. Wilt3, and S. A. Ringel1 1 Department of Electrical Engineering, The Ohio State University, 2015 Neil Avenue, Columbus, OH 43210, USA 2 Department of Physics, The Ohio State University, Columbus, OH 43210, USA 3 NASA Glenn Research Center, Cleveland, OH 44135, USA ABSTRACT Si-doped InAsxP1-x layers with As mole fractions ranging from 0.05 to 0.50 were grown on InAsxP1-x step-graded buffer layers on InP substrates by solid source molecular beam epitaxy. The growth parameters consisted of a P:In flux ratio of 7:1, a growth temperature of ~ 485oC, a growth rate of 2.2 Å/s, and an As:In flux ratio of 0.37-2.36 for varying As mole fractions. The As mole fraction and the layer relaxation were determined using triple axis x-ray diffraction measurements. Near complete relaxation (>93%) was achieved for all Si-doped InAsxP1-x epilayers. The structural morphology indicated that the InAsxP1-x graded buffer layers were effective in relieving the lattice mismatch strain as evidenced by a well-developed crosshatch morphology and low rms surface roughness. The electron concentration, mobility, and Si donor activation energy for each InAsxP1-x composition were determined using temperature dependent Hall measurements. At a constant electron carrier concentration of ~3.5x1016 cm-3, the 300 K carrier mobility increased from 2700 to 4732 cm2/V-sec with increasing As mole fraction from 0.05 to 0.50. INTRODUCTION InAsxP1-x alloys are receiving attention for electronic and optoelectronic applications due to the wide range of attainable bandgap energies from 0.36 eV to 1.35 eV. Experimental determination of both the electronic and structural properties of bulk, relaxed InAsP layers at various bandgap energies, thus varying As mole fractions, are critical for attaining optimum device performance. Growth studies of strained, mixed-anion material systems, such as InAsxP1x/InP [1], GaAsxP1-x/GaP [2], and GaAsxP1-x/GaAs [3] indicate that the strain at the surface of the growing thin film modifies the growth dynamics in order to reduce the strain in the film. For strained InAsxP1-x, this is achieved by a reduced incorporation coefficient of As into the alloy and also an As-P exchange reaction that produces rough interfaces [4,5]. This paper presents a systematic study of structural and electronic properties of relaxed Si-doped InAsxP1-x alloys grown on step graded InAsxP1-x buffers by solid source molecular beam epitaxy (SSMBE) and the dependence of the carrier concentration, mobility, and Si donor activation energy on As composition in InAsxP1-x alloys. EXPERIMENTAL PROCEDURE Si-doped InAsxP1-x layers with As mole fraction ranging from 0.05 to 0.50 were grown on InAsxP1-x step-graded buffer layers on (100) InP substrates using a SSMBE system equipped with conventional Group III cells and valved cracker sources for both arsenic and phosphorous. To accommodate the large lattice mismatch
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