Quantitative Analysis of Absorption and Field-Induced Absorption Changes in InGaN/GaN Quantum Wells

Abstract

Results of absorption and electroabsorption measurements are reported for wurtzite InGaN/GaN quantum wells. Despite the relatively high exciton binding energy of 25 meV in GaN no pronounced excitonic features could be observed and the absorption spectra are very similar to those obtained for bulk material. The measured field-induced absorption changes are as large as 7000 cm -1 below and 20000 cm -1 above the band edge. A quantitative analysis of electroabsorption data allows the precise determination of the strong internal fields in InGaN/GaN heterostructures originating from strain-induced polarization and differences in the spontaneous polarization. The fields measured on functioning diodes vary between 1.1 MV cm -1 and 1.4 MV cm -1 for indium concentrations in the InGaN quantum wells ranging from about 7 to 9%.