Lasing of semi-polar InGaN/GaN(1122) heterostructures grown on m-plane sapphire substrates

Abstract

Results for long-wavelength emitters are presented for semi-polar InGaN/AlGaN/GaN heterostructures grown on GaN(1122)/m-sapphire templates by metalorganic chemical vapor deposition. The semi-polar GaN layers were 10 to 25 μm thick and grown by HVPE on sapphire substrates. X-ray diffraction measurements indicated high crystallographic quality that approaches that of GaN(0001) layers on sapphire. A comparison based on optical pumping experiments, low- and high-density excitation photoluminescence experiments, and atomic force microscopy is drawn between InGaN/GaN quantum well laser heterostructures grown by metalorganic vapor phase epitaxy either on either polar GaN(0001)/c-sapphire or on semi-polar GaN(1122)/m-sapphire. C-plane InGaN/GaN/sapphire structures exhibited low threshold pump power densities < 500 kW/cm² for emission wavelengths up to 450 nm. For laser structures beyond 450 nm the threshold pump power density rapidly increased resulting in a maximum lasing wavelength of 460 nm. Semipolar InGaN/GaN(1122)/m-sapphire structures showed a factor of 2-4 higher threshold pump power densities at wavelengths below 440 nm which is partly due to lower crystalline perfection of the semi-polar GaN/sapphire templates. However, at longer wavelengths > 460 nm the threshold power density for lasing of semi-polar heterostructures is less than that for c-plane heterostructures which enabled rapid progress to demonstration of lasing at 500 nm wavelength on semi-polar heterostructures. The absence of V-type defects in semi-polar, long-wavelength InGaN/GaN structures which are usually present in long-wavelength c-plane InGaN/GaN structures is attributed to this phenomenon.