研究目的
To suppress wafer bowing and crack generation of GaN on Si substrates by investigating the effects of the Al content and thickness of the AlGaN interlayer on the compressive strain in the overlying GaN layer.
研究成果
The study demonstrated that AlGaN interlayers can control compressive strain in GaN layers on Si substrates to reduce wafer bowing and cracks. An ideal relaxation ratio exists for maximal constant strain, but experimental values were lower than simulated. Despite this, AlGaN interlayers with near-optimal Al content reduced the strain decrease rate in GaN, indicating potential for improved strain management in epitaxial growth.
研究不足
The simulation did not consider effects of surface roughness or generation of threading dislocations in Al(Ga)N interlayers. Experimental relaxation ratios were smaller than simulated, possibly due to inaccurate critical thickness estimation, Ga mixing in AlGaN growth, or differences between high-temperature and room-temperature strain evaluations. Noise in curvature data limited the resolution of initial strain transients.
1：Experimental Design and Method Selection:
The study used a combination of simulation and experimental methods. Simulation was conducted using commercial software (STREEM AlGaN, STR Group) with equilibrium and kinetic stress relaxation models. Experiments involved metalorganic vapor phase epitaxy (MOVPE) growth on Si substrates with in situ curvature monitoring and ex situ characterization via reciprocal space mapping (RSM) of X-ray diffraction (XRD).
2：Sample Selection and Data Sources:
2-inch Si(111) substrates with sputtered AlN buffer layers were used. Samples included GaN template layers, Al(Ga)N interlayers, and GaN layers grown with varying Al contents and fixed thicknesses.
3：List of Experimental Equipment and Materials:
Equipment includes a horizontal single-wafer MOVPE reactor (AIX 200/4 RF-S, AIXTRON), in situ curvature monitoring system (EpiCurve?TT SP Blue AR 3W, LayTec), and XRD for RSM. Materials include trimethylgallium (TMGa), trimethylaluminum (TMAl), ammonia (NH3), and H2 carrier gas.
4：Experimental Procedures and Operational Workflow:
Growth was performed at 1100 °C with pressures of 200 mbar for GaN and 50 mbar for Al(Ga)N. Strain was calculated from curvature data using Stoney's formula, and relaxation ratios were evaluated from RSM measurements.
5：Data Analysis Methods:
Strain transients and dislocation densities were analyzed from simulation outputs. Experimental data were averaged to reduce noise, and comparisons were made between simulated and measured values.
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