High-Voltage GaN p-n Junction Diodes with Low Leakage Current

在本研究中，研究了电激活掺杂在MOCVD生长GaN中的Mg受体的最佳后快速退火（RTA）条件。众所周知，MOCVD生长的掺镁氮化镓具有高电阻率，除非样品在晶体生长后进行退火。这是由于氮化镓中Mg受体的H钝化所致。到目前为止，还没有研究过镁浓度对最佳退火条件的影响。结果表明，氮化镓中Mg掺杂浓度不同，退火温度也不同。结果表明，无论Mg掺杂浓度在1.25x10^<19>和1x10^<20>cm^<-3>之间，室温下的最大空穴浓度都在8x10^<17>cm^<-3>左右。当样品在200℃下进行表征时，掺杂1.25 × 10^<19>cm^<-3>的样品活化效率最高，达到80%以上。高温下的电特性表明，过量的高温退火导致大量Mg掺杂的GaN样品产生与Mg相关的供体水平，导致Mg受体在高温下的活化降低。这就是为什么2.5x10^<19>cm^<-3>和5x10^<19>cm^<-3>的掺镁GaN样品在750℃和650℃退火时，空穴浓度分别为8x10^<17>cm^<-3>的最大原因。基于上述结果，制备了p-n结二极管。n-GaN的掺杂浓度选择为5x10^<17>cm^<-3>。二极管击穿电压均大于100V，且随着测量温度的升高而升高，表明击穿机制为雪崩击穿。结果表明，估计击穿场高达2.9MV/cm，非常接近3.3MV/cm的理论极限。我们相信这些结果为用p型材料制造gan基电子器件提供了有用的设计参数信息。

In this research work, the optimum post rapid thermal annealing (RTA) conditions have been investigated to electrically activate Mg acceptors doped in the MOCVD grown GaN. It is widely known that the MOCVD as-grown Mg-doped GaN shows high resistivity unless the sample is annealed after crystal growth. This is due to the H passivation of Mg acceptors in GaN. So far, the optimum annealing conditions have not been studied depending on the Mg concentration. It was found that there was an optimum annealing temperature depending on the Mg doping concentration in GaN. Results showed that the maximum hole concentration at room temperature was about 8x10^<17>cm^<-3> regardless of the Mg doping concentration between 1.25x10^<19> and 1x10^<20>cm^<-3>. A maximum activation efficiency of over 80 % was obtained for the sample doped with 1.25x10^<19>cm^<-3> when the sample was characterized at 200℃. Electrical characterization at elevated temperatures revealed that excessive high temperature annealing for heavily Mg-doped GaN samples resulted in Mg-related donor level generation, leading to the reduced Mg acceptor activation at elevated temperatures. This is the reason why Mg-doped GaN samples with 2.5x10^<19>cm^<-3> and 5x10^<19>cm^<-3> exhibited a maximum hole concentration of 8x10^<17>cm^<-3> annealed at 750℃ and 650℃, respectively.Based on the above results, p-n junction diodes have been fabricated. The doping concentration in n-GaN was chosen to be 5x10^<17>cm^<-3>. The breakdown voltage of the diodes was more than 100V and it increased with increasing the measurement temperature, suggesting the breakdown mechanism is due to avalanche breakdown. It was found that the estimated breakdown field was as high as 2.9MV/cm, which was proved to be very close to the theoretical limit of 3.3MV/cm.We believe that these results provide useful information as design parameters for the fabrication of GaN-based electronic devices with p-type materials.