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Influence of trimethylaluminum predoses on the growth morphology, film-substrate interface, and microstructure of MOCVD-grown AlN on (111)Si
摘要： Aluminum nitride (AlN) was deposited on (111) silicon by metalorganic chemical vapor deposition after varied trimethylaluminum predoses. Growth morphologies, film-substrate interfaces, and film microstructures were examined using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. In samples grown with predoses, lateral growth was observed over faceted "patches" formed during the predose. Three-dimensional growth was observed to seed from small islands on the surface of these patches and eventually overgrow them. The three-dimensional growth mode was similar to that observed when AlN was grown without a predose, resulting in similar morphologies in all films, regardless of predose, after the islands coalesced. The AlN-silicon interface was found to be predominantly amorphous when no predose was used. However, narrow regions were observed over which the film was in atomic registry with the substrate. This indicates AlN nucleates in epitaxy with the substrate and amorphous silicon nitride forms between nucleation sites due to ammonia exposure. Films grown with predoses had structurally abrupt interfaces, suggesting aluminum within the observed patch features inhibits the reaction between ammonia and silicon at the onset of growth. A structure distinct from both wurtzite AlN and diamond cubic silicon was observed at the substrate interface in films grown with a predose, consistent with either zinc blende AlN or a strained Si/Al alloy. A mosaic microstructure was observed in all films, grown with or without predoses, which consisted of sub-boundaries formed by clusters of threading dislocations. Threading dislocations, separated by hundreds of nanometers, were found to be tilted along common directions, providing evidence for a dislocation bending mechanism possibly enhanced by the predose.
关键词： Defects,Crystal morphology,Metalorganic chemical vapor deposition,Semiconducting aluminum compounds,Nucleation,Nitrides
更新于2025-09-19 17:15:36
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Compensation effects of high oxygen levels in semipolar AlGaN electron blocking layers and their mitigation via growth optimization
摘要： InGaN-based laser diodes (LDs) grown on the semipolar plane of GaN offer advantages arising from predicted higher gain compared to c-plane devices. However, the performance of semipolar devices has been limited by low injection efficiency. In prior work, this has been proposed to be caused by an inefficient AlGaN electron blocking layer (EBL). A high oxygen level in the EBL found in previous work could cause compensation of the p-type dopants. In this work the oxygen impurities were eliminated via optimizations during the metalorganic chemical vapor deposition (MOCVD) growth. Optimization of the V/III ratio and an increase in the growth temperature during the AlGaN growth was found to reduce the oxygen incorporation. Additionally, residual sources of oxygen were removed from the MOCVD growth process. These combined steps reduced the peak oxygen level in the AlGaN from 5 × 1018/cm3 to 6 × 1017/cm3 as measured by secondary ion mass spectroscopy. LDs were fabricated with and without these modifications to clarify the effect of the reduced oxygen. The threshold current and differential efficiency showed improvement with reduced oxygen. The internal loss and gain of these LDs were measured using the segmented contact method, confirming that the injection efficiency was boosted from 60% with high oxygen to 80% with low oxygen.
关键词： B2. Semiconducting aluminum compounds,A3. Metalorganic chemical vapor deposition,B3. Laser diodes,B1. Nitrides,A1. Impurities
更新于2025-09-09 09:28:46