Absorption of InGaN Single Quantum Wells Determined by Photothermal Deflection Spectroscopy

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Abstract
Photothermal deflection spectroscopy (PDS) is used to study the absorption of GaN/InGaN/GaN double heterostructures in the energy range from 0.6 to 3.8 eV. The heterostructures containing 1–77-nm-thick InGaN single quantum wells were deposited by chemical vapour deposition from organometallic precursors. They are measured to investigate the absorption coefficient, bandgap, indium concentration and fluctuation of the quantum wells. A bandgap increase of hexagonal In x Ga1-x N (x≈0.14) of 60 meV is observed with decreasing well thicknesses from 15 to 1 nm. The distribution of In-concentration of the In x Ga1-x N layers was estimated from the slope of the absorption coefficient versus photon energy for energies below the bandgap and found to be Gaussian with a full width of half maximum of Δx=0.03.