Reducing dislocations of Al-rich AlGaN by combining AlN buffer and AlN/Al0.8Ga0.2N superlattices

Structural and optical properties of Al0.69Ga0.31N films are greatly improved by combining special-designed AlN buffer and AlN/AlGaN superlattices (SLs) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The optimized AlN buffer grown under lower V/III ratio provides a template with low screw threading dislocations (TDs), and the partially relaxed SLs play a role of dislocation filter for the edge ones. Thus, the combinative use of both buffers effectively reduces both screw and edge TDs in Al-rich AlGaN, which has been evidenced by cross-sectional transmission electron microscopy (TEM). It is found both (0 0 0 2) and (1 0 1¯ 5) full-width at half-maximum (FWHMs) of Al0.69Ga0.31N epilayer are decreased to 173 and 703 arcsec, respectively. Meanwhile, enhanced near band edge (NBE), photoluminescence (PL) and suppressed deep level emission measured at 30 K further confirm the effects of the combinative buffers on improving optical quality of Al0.69Ga0.31N films.