Comparison of gain in group-III-nitride laser structures grown by metalorganic vapour phase epitaxy and plasma-assisted molecular beam epitaxy on bulk GaN substrates

摘要

Light amplification features of similar group-III-nitride laser structures grown by metal organic vapour phase epitaxy (MOVPE) and plasma-assisted molecular beam epitaxy (PAMBE) as alternative techniques were investigated. The samples are characterized by very low dislocation density (10~5 cm~(-2)) that results from the use of high-pressure-grown GaN substrates. Gain measurements were carried out by means of the variable stripe length method. A maximum excitation power of 464 kW cm~(-2) corresponds to a peak modal gain value of 180 cm~(-1) for the MOVPE-grown sample and 315 cm~(-1) for the PAMBE-grown one. Saturation lengths of 350 μm and 250 μm measured for MOVPE- and PAMBE-grown samples, respectively, indicate reduced nonradiative recombination compared to heteroepitaxy on foreign substrates. Activation energies associated with InGaN band profile fluctuations derived from temperature-dependent photoluminescence measurements yield values of 41 meV and 22 meV for MOVPE and PAMBE, respectively. Improved band profile smoothness is accompanied by a reduced threshold for stimulated emission in favour of the PAMBE-grown laser.