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

在这项研究工作中，最佳后快速热退火（RTA）条件进行了研究，以电激活Mg受主掺杂在MOCVD生长的GaN。众所周知，MOCVD生长的Mg掺杂GaN显示出高电阻率，除非在晶体生长后对样品进行退火。这是由于GaN中Mg受体的H钝化。到目前为止，还没有根据Mg浓度研究最佳退火条件。结果表明，GaN中Mg的掺杂浓度不同，存在一个最佳退火温度。结果表明，在室温下的最大空穴浓度为约8x 10 - <17>4cm-3，<-3>而与1.25x10 - 4cm-3和1x 10 - 4cm-3之间的Mg掺杂浓度无关<19><20><-3>。当掺杂量为1.25 × 10 ~（13）cm ~ 3时，在200℃下的活化效率最高可达80%以上<19><-3>。在高温下的电特性表明，过度的高温退火的重Mg掺杂的GaN样品导致在Mg相关的施主能级的产生，导致在高温下的Mg受体的激活减少。这就是为什么Mg掺杂的GaN样品在750℃和650℃退火时，空穴浓度分别为2.5 × 10 ~（-3）cm <19>~ 2<-3>和5 × 10 <19><-3>~（-3）cm ~ 2时的最大空穴浓度为8 × 10 ~<17><-3>（-3）cm ~ 2的原因。n-GaN中的掺杂浓度被选择为5 X 104 <17>cm-3<-3>。二极管的击穿电压均大于100 V，且随温度升高而升高，表明其击穿机理为雪崩击穿。计算结果表明，该器件的击穿场强高达2.9MV/cm，与理论极限3.3MV/cm非常接近，为p型材料GaN基电子器件的设计提供了参考。

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.