Reduction of V-pit density and depth in InGaN semibulk templates and improved LED performance with insertion of high temperature semibulk layers

Abstract

Highly relaxed InGaN templates with an effective In-content of ~ 10% that exhibit reduced V-pit density and an improved surface roughness are reported using the semibulk (SB) growth approach. This was achieved by the insertion of 5-period high temperature InGaN semibulk (HTSB) regions. This report demonstrates that better quality InGaN templates can be achieved by the insertion of HTSB within the templates, rather than by ending the templates with a superlattice structure (SLS) or by refilling the pits with GaN interlayers. Three SB samples were grown with and without the HTSB layers. Using secondary-ion mass spectrometry, photoluminescence, and x-ray diffraction, the effective In-content of the templates was determined to be 9.6%, 5.8%, and 8.7%. Using atomic force microscopy, the surface roughness was found to improve from 4.4 nm to 1.7 nm by using the two HTSB regions, and the average V-pit density and depth improved from 7.6×10-7 cm-2 to 4.5×10-7 cm-2 and 8.2 nm to 2.8 nm, respectively. Also, the maximum V-pit depth was reduced from about 30.5 nm to about 9.6 nm in the sample with the HTSB regions. Two LEDs were studied, one with both HTSB regions, and one with only the topmost HTSB. The optical power density of the LED with both HTSB regions was 1.4 times higher at the peak injection current, displayed a ~1.3 times higher external quantum efficiency peak, and a delay of the EQE droop onset. These results show that higher In-content SB templates can be improved with the implementation of a modified growth approach.