Excess Carrier Lifetime Measurements for GaN on Sapphire Substrates with Various Doping Concentrations and Surface Conditions by the Microwave Photoconductivity Decay Method

Abstract

ABSTRACTWe have measured excess carrier lifetimes in GaN with various doping concentrations and surface conditions by the microwave photoconductivity decay method. GaN samples were grown by metalorganic chemical vapor deposition (MOCVD) without intentional doping and with Si doping or Mg doping on a-face sapphire substrates. By using the microwave photoconductivity decay method, we obtained 1/e excess carrier lifetimes of larger than 50 μs for the Si doped and undoped GaN and of less than 10 μs for the Mg doped GaN. We changed surface conditions for the samples by the inductively coupled plasma (ICP) etching and investigated effects of surface conditions on the carrier recombination behavior. The ICP etching has negligible effects on carrier lifetime in the Si doped GaN. On the other hand, in the undoped GaN, the ICP etching lengthened the carrier lifetime compared with the as-grown sample. On the contrary, the ICP etching shortened the carrier lifetime in the Mg doped GaN. The ICP etching seems to form hole traps and recombination centers at GaN surfaces and thus the carrier lifetime became longer in the undoped GaN and shorter in the Mg doped GaN.