Electroabsorption Spectroscopy ? Direct Determination of the Strong Piezoelectric Field in InGaN/GaN Heterostructure Diodes

Abstract

We report on room temperature electroabsorption measurements on (In)GaN heterostructure p–i–n diodes. This technique allows a precise determination of the strong changes of internal fields at the InGaN/GaN hetero interface due to differences in the spontaneous polarisation and strain-induced piezoelectric fields. The measured fields vary between 1 and 1.4 MV/cm for thin InGaN layers with an In content ranging from approximately 7% to 9%. Absorption spectroscopy is also well suited to investigate the optical properties of GaN layers. In contrast to Si-doped or intrinsic material Mg-doped GaN films reveal a pronounced absorption tail below the band edge with absorption coefficients of about 30 cm—1 at typical emission wavelengths (λ ≈ 400 nm) of InGaN laser diodes.