Luminescence Studies Of C Implanted And C+Si And C+Mg Coimplantd N-type GaN

Gallium nitride(GaN)is an important wide energy gap semiconductor material with good properties.The films growth,GaN-based devices,and the formation and energy levels of point defects in GaN are investigated.Carbon is often present in GaN films as a residual impurity,and is also intentional doped to produce p-type GaN.C is believed to have significant effects on the optical and electrical properties of GaN. In this paper,the luminescences of C implantation and C+Si and C+Mg coimplantation in unintentional doped n-type GaN are studied.Three kinds of GaN samples were used in the experiments.In their as-grown states,#1 samples had YL(yellow luminescence),#2 samples had strong YL,and #3 samples had no YL.C ions were implanted in samples at room temperature with different doses from 1.0×10¹³to 1.0×10¹⁷cm^-2,while C+Si and C+Mg were implanted with doses from 1.0×10¹³to 1.0×10¹⁶cm^-2.Post-annealing was done in a quartz open-tube furnace in a flowing N₂ gas for 30 min at 950℃.By the measurements and analyses of photoluminescence spectra and micro-Raman spectra, the influences of C implantation on YL and NBE(near band edge)emissions,as well as the influences of C+Si and C+Mg coimplantation on YL and RL(red luminescence) in n-type GaN are studied.The origins of YL,RL and NBE emissions are given and explained.The experiment research of C implantation suggests that C can enhance YL in #3 GaN effectively.In addition to V_Gaand V_Ga-O_N complex,C_i or C_i-C_N complex is another deep-level center associated with YL in GaN.With the increasing of the implantation dose,i.e.,with the increasing of the level of implantation-produce lattice damage at the dose of 1.0×10¹⁷cm^-2,the diffusivity of C_i becomes poor.Consequently, the concentration of C_i or C_i-C_N complex is enhanced,which could make the YL intensity of#1,#2 and #3 GaN increase.Based on the experiment result that the peek of the NBE emission shift towards high-energy direction with increasing C implantation dose,the NBE emission is attributed to the transitions of bound exciton(bound to a shallow donor V_N)and DAP (a shallow donor to shallow accepter pair).The shift of the peek of the NBE emission is thought to be induced by the variety of the V_N concentration at different implantation dose.In addition,the experiment result of C implantation in #2 GaN shows that, compared with the unimplanted sample,YL of C implanted samples exhibited marked reductions,while the near band edge(NBE)emissions were reduced in less extent. The result is believed to be caused by the strong adsorption on the GaN surface for the migrating point defects involved in YL during ion implantation.The adsorption is weaken with the increasing of ion implanted depth.The study of the C+Si and C+Mg coimplantation shows that Mg doping suppresses YL in GaN effectively.V_Gaand V_Ga-O_N complex are thought to be related with RL in GaN.With the increasing of C implantation dose,more and more C ions form C_Ga,and the RL intensity is reduced obviously.Hence,C implantation can suppress RL in GaN at high doses(≥10¹⁵cm²).