Photoreflectance and Photoinduced Microwave Reflectance Studies of Surface Band Bending in Mg-doped InN

Photoreflectance (PR) and microwave-reflectance photoconductivity-decay (μ-PCD) have been applied to study the surface band bending in Mg-doped InN layers with various Mg concentrations (∼1 × 1017 to ∼7 × 1019 cm−3) and thicknesses (∼400 to ∼3600 nm). A PR resonance related to the band-to-band transition at the Γ point below the surface electron accumulation is observed for moderately doped samples ([Mg]: 1.3 × 1017 cm−3 to 8.7 × 1017 cm−3). Samples with the Mg doping concentration in the range of ∼5 × 1018 ≤ [Mg] ≤ 7 × 1019 cm−3 are p-type and show very weak or no PR resonance. It is shown that the results correlate with the surface layer depletion thickness. The strongest PR signal is observed for thick depletion layers. The results are confirmed by μ-PCD measurements that show the longest carrier lifetimes for moderately doped samples with the thickest surface depletion layer.