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We investigated the dependence of n-type carriers at the interface between InP substrates and epitaxial layers grown by MOCVD on the phosphine (PH3) partial pressure and the growth temperature sequence. The carrier concentration decreases with increasing the PH3 parrial pressure, The carrier concentration also reduces when the temperature during thermal etching is high, and the temperature during the initial growth stage is low. Silicon and oxygen were detected as impurities at the interface by secondary ion mass spectrometry (SIMS) measurement. The silicon concentration is no less than 1~1 0~~c m -~ under all growth conditions. The oxygen concentration varied from 1~10~7cm-3 to 8~1O~gcm-3 and had no relationship with the carrier concentration. htroductionThere is a great deal of interest recently in the epitaxial growth on semi-insulating InP substrates. This occurs largely because of the importance of fabrication of the high frequency devices such as high electron mobility transistors. It is known that there are n-type carriers at the interface between substrates and buffer layers [l-61. Rakennus et al. and Knauer et al. [3,6] have shown that these carriers reduce the mobility in homo-epitaxial layers on InP substrates. In the case of MBE epitaxial layer on GaAs substrates, Izumi et al. [7] have shown that n-type carriers cause the poor pinch-off characteristics and the current leakage in the MESFET between ohmic metals and epitaxial layers. In this study, we have investigated the dependence of n-type carriers on the PH3 partial pressure and the growth temperature sequence. Experimental 140A low pressure MOCVD system was used for growing InP epitaxial layers on Fe-doped InP substrates. These substrates were etched using H2S04:H202:H20 (5:l:L 1 min., at RT.). 0.7 pm thick undoped InP was grown as a buffer layer, followed by 0.3 pm thick S-doped InP with the carrier concentration of about 7~10~7cm-3. The pressure was 30 torr and the total flow &e was 15 Vmin. Trimethylindium (TMI) and PH3 were used as source materials. Fig. 1 shows the sequence of epitaxial growth in this study. TWQ types of PH3 partial pressure sequence ((a)@)) and three types of growth temperature sequence ((A),(B) and (C)) were used. Surface morphology was observed by a Normaski microscope. An electrochemical capacitance-voltage (ECV) profiler and a SIMS were applied for the measurement of carrier and impurity concentrations at the interface between substrates and undoped InP layers. ResultsAll epitaxial layers grown in this study had mirrorlike surfaces. The carrier concentration at the interface however strongly depended on the growth sequence. Fig. 2 shows an ECV profile under the condition of sequence (B)-(b). N-type carriers exist at the interface and the peak value of the concentration was 5 . 0~1 0~~c m *~ . Table 1 summarizes carrier concentrations at the interface under various growth conditions. The carrier concentration decreases with increasing the PH3 partial pressure. In the case of the temperature sequence B, the carrier concent...
The effect of various InP substrates properties on epitaxial layer quality was investigated. From the results of experiments on MOCVD, we found that the average haze of epitaxial layer surfaces measured by surfscan can be reduced by using substrates with optimum surface mis-orientation angles of 0.05-0.10 degrees. Our experiments on MBE also showed a similar tendency. Furthermore it was found that appropriate treatment of substrates prevents slips on the periphery of epitaxial wafers.
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