Defect Model and Growth Characteristics of Low Temperature GaAs
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DEFECT MODEL AND GROWTH CHARACTERISTICS OF LOW TEMPERATURE GaAs
M. FATEMI*, B. TADAYON, H.B. DIETRICH', and S. TADAYON'" *Electronics Science and Technology Division, U.S. Naval Research Laboratory Washington, D.C. 20375-5000; "**COMSAT Laboratory, Clarksburg, MD 20871 ABSTRACT Low-temperature GaAs layers (LTGaAs) grown by molecular beam epitaxy on GaAs substrates have been characterized by x-ray diffraction techniques. X-ray rocking curve measurements on more than 200 anneal conditions show that through appropriate choice of growth condition, layers with different states of strain are obtained. Three distinct ranges of low temperature growth are defined, labelled as "low-range," "mid-range," and "high-range," corresponding to growth temperatures less than 260 TC, between 260 and 450 TC, and more than 450 'C, respectively. 0.5 pm thick films grown in the low-range are amorphous, whereas those in the mid-range are fully strained and lattice-matched to the substrate, and those grown above 450 "C are indistinguishable from ordinary GaAs. Notable properties of mid-range layers are the random behavior of the as-grown strain, and the expansion and contraction of the lattice parameter with thermal anneals up to 900 'C. A growth model for LTGaAs based on arsenic antisite defects is proposed. INTRODUCTION The molecular beam epitaxy (MBE) growth of As rich GaAs layers at low temperatures on GaAs (LTGaAs) was reported recently ".3.The interesting physical and electronic properties of these and similar low-temperature IlI-V compounds make the materials potentially useful for a wide range of device applications. Among these properties are reduced recombination times of about 400 fs, suitable for integrated sub-picosecond optoelectronic switches, and their high breakdown voltage, useful for power field effect transistors (FET's).4 5. It was shown by transmission electron microscopy in Ref 1 that the layers are highly perfect and contain only a few dislocations. In addition, x-ray rocking curves from a sample grown at 200 0C showed a second diffraction peak at an angle slightly lower than that of the substrate. This peak was interpreted as that of a relaxed cubic lattice with a lattice parameter slightly larger than, and supported by the GaAs substrate which is also cubic. However, an interface dislocation network which is nearly always present in mismatched systems was not reported. The concept of a relaxed cubic lattice appeared to be in conflict with the absence of misfit and threading Mat. Res. Soc. Symp. Proc. Vol. 241. @1992 Materials Research Society
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dislocations, as seen from transmission electron microscopy (TEM). A study of the behavior of the lattice parameter and electrical properties was also reported recently. 6 In our study, these findings were examined in greater detail. In particular, we wished to ascertain the possibility of a wider range of growth temperatures about 200 'C for this material. It was also desirable to calibrate the growth temperatures more exactly, so that wafers obtained from different s
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