High to Ultrahigh Si-Doped GaN Grown by Metalorganic Chemical Vapor Deposition at 550 °C for Heterogeneous Integration

Abstract

The heterogeneous integration of IIl-nitride materials with other semiconductor systems for electronic devices is attractive because it combines the excellent electrical properties of the Ill-nitrides with other device platforms. Pursuing integration through metalorganic chemical vapor deposition (MOCVD) is desirable because of the scalability of the technique, but the high temperatures required for the MOCVD growth of Ill-nitrides (>1000 °C) are incompatible with heteroepitaxy on some semiconductor systems and fabricated wafers. Thus it is critical to develop IIl-nitride films with good electrical properties at growth temperatures compatible with temperature sensitive substrates. High crystal quality GaN films with reduced impurity levels have been achieved at temperatures as low as 500 °C using pulsed growth methods such as atomic layer epitaxy and flow modulation epitaxy (FME). However, the electrical behavior of doped LT Ill-nitride films is relatively unexplored. In this work, thin Si-doped LT GaN films were grown at 550 °C by atmospheric pressure MOCVD using an FME scheme. Triethylgallium and ammonia were used as the GaN precursors and disilane as the Si dopant. Because of the very low growth rate (0.006 A/s), 1200 FME cycles resulted in approximately 16 nm-thick films. Two different FME Si-doping schemes were investigated. The first series varied the fraction of cycles in which disilane was injected into the growing film. Samples were grown with disilane injected every 20, 10, 5, 3, 2, and 1 cycle. The second series varied the disilane flow while using the standard frequency of disilane injection (1 in 5 cycles). Samples were characterized by Hall measurements and secondary ion mass spectrometry (SIMS). For the disilane injection series films, electron concentrations up to 6.97 x 4018 om”? were achieved, with electron mobilities from 34 to 119 cm vi sl The peak electron concentration was achieved for the sample with disilane injected in 1/3 of FME cycles during growth. The charge dropped off for samples with higher frequencies of disilane injection, likely because of degraded morphology. The Si concentrations measured by SIMS were somewhat higher than the electron concentrations measured by Hall. The background atmospheric impurity concentrations averaged 2.1 xX 1017 em’? for oxygen and 3.9 x 10 0 cm ~ for carbon, with no apparent dependence on Si concentration. The disilane flow series resulted in films with electron concentrations from 5.98 x 10 ~ cm ~ to 5.91 x 10'9 om”? and electron mobilities from 52 to 115 cm? vi s |, with the highest charge achieved with the highest disilane flow. The sheet resistance of this sample was 1068 Q/#, which is comparable to low resistance GaN films grown at high temperature, which range from 100-500 Q/#. These results demonstrate the potential for LT Ill-nitrides in electronics applications. This work supported in part by Intel Corporation and the Solid State Lighting and Energy Electronics Center.