SUB-BANDGAP ABSORPTION OF GALLIUM NITRIDE DETERMINED BY PHOTOTHERMAL DEFLECTION SPECTROSCOPY

Photothermal Deflection Spectroscopy (PDS) is used to study the sub-ba ndgap absorption of hexagonal gallium nitride (GaN) in the energy rang e from 0.6 to 3.8 eV. Auto-, n- and p-doped GaN layers deposited by ch emical vapour deposition from organometallic precursors (MOCVD) or ele ctron cyclotron resonance assisted molecular beam epitaxy (ECR-MBE) ar e measured to investigate the optical band edge, the sub-bandgap absor ption and the absorption due to free carriers. PDS is also useful to s tudy the long term and thermal stability of GaN. Changes in sub-bandga p absorption by heating the samples to 600 degrees C for several hours are presented.