Traps in MOCVD n-GaN Studied by Deep Level Transient Spectroscopy and Minority Carrier Transient Spectroscopy

摘要

Electron and hole traps in MOCVD n-GaN have been studied using deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). Sidoped GaN is grown on sapphire, free-standing n~+-GaN and SiC substrates. DLTS and MCTS measurements are performed for Schottky diodes, p+n diodes and MOS structures. A total of nine electron traps are found in the trap energy depth ranging from 0.24 to 1.2 eV with the trap concentration ranging from 10~(12) to 10~(16) cm~(-3), while a total of five hole traps in the trap energy depth from 0.25 to 1.8 eV with the trap concentration from 10~(14) to 10~(16) cm~(-3). The variation of trap concentrations are discussed in relation to the substrates used. Interface state densities around 1012 cm~(-2)eV~(-1) are obtained for MOS structures on sapphire and n~+-GaN substrates. In carbon-doped n-GaN on SiC, a hole trap with the energy depth of 0.86 eV is observed with the trap concentrations around 1016 cm~(-3), suggesting that this hole trap is carbonrelated. Moreover, a trap with the energy depth of 0.88 eV is detected in high resistivity GaN doped with carbon using optical current DLTS. It is found that traps with the energy levels at Ec-0.57 and Ev+0.86 eV have larger trap concentrations in MOCVD n-GaN, while a trap at Ev+0.86 eV is dominant in carbon-doped n-GaN.