Investigation of optimized ohmic contact of direct ITO layer with synchrotron radiation analysis

With application of the current transport enhanced layer (CTEL) on the top of p‐type GaN, we optimized process conditions, which show the contact resistance of 1.43x10–3 Ω·cm2, using ITO contact layer that has advantages in the enhancement of light extraction efficiency. High‐resolution near edge X‐ray absorption spectroscopy was used to investigate the interface reaction between GaN / CTEL and ITO layers. Interstitial molecular N2 was directly observed by vibrationally resolved N'K‐edge absorption spectroscopy. It is suggested that GaN was chemically changed to gallium oxide (Ga2O3) and nitrogen molecule (N2) [2Ga‐N + 3/2 O2 => Ga2O3+N2] during annealing process, and this newly formed layer makes depletion width narrowing for the tunneling properties for the ohmic contact. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)