Research On Si Doped Double Channel And Multi-channel Al Ga N/ga N Heterojunction Material Properties

Owing to the advantage of wide bandgap, high saturated electron velocity and high breakdown field strength, Ga N and other Group III nitrides have been the first of all materials for high voltage and high frequency devices. After years of exploration and efforts, the crystalline quality and electrical characteristics of Ga N is better and higher than ever. The growth mechanism and the related theories of Ga N material have been more and more complete. However, as so far, the applications of Ga N-based devices is dominated by high electron mobility transistor(HEMT) with single heterojunction Al Ga N/Ga N structure. Many researchers are working hard in exploring new device structures which including the multi-channel heterojunction stucture. There are important implications in studying the multi-channel heterojunction structure that multi-channel heterojunction structure has superior performances on enhancing the 2DEG and modulating the 2DEG to the single heterojunction Al Ga N/Ga N structure.In this paper, the growth and the properties of the doped Ga N body material and the double channel Al Ga N/Ga N heterojunction structure with doped barrier layer is investigated, and the characteristics of the ten channels Al Ga N/Ga N heterojunction structure is also studied.Here are the results.1. The Ga N body materials with different concentration Si doped are grown by using the MOCVD320 system developed independently. Through the material characterization, it is found that doping efficiency is different with different doping order.The material surface morphology getting worse and the edge dislocation getting more as the doping content growing with a high Si doping level, while the screw dislocation almost unchanged. The roughness is 0.39 nm in 5×5μm2 scanning area while the Si doping concentration is 5.0×1018cm-3, the concentration of the edge dislocation and the screw dislocation are 2.63×109cm-2 and 5.7×107cm-2, respectively. Doping of Si makes the Ga N lattice constant c reduce to Ga N lattice constant c with no strain, and reduces in-plane stress in the Ga N.2. The double channel Al Ga N/Ga N heterojunction structures with different concentrations of Si doped lower barrier layer are grown on the sapphire substrate. It is found that with increasing doping concentration, screw dislocation density first increases and then decreases. The doping changes the tensile strain between the upperand lower barrier layer, redistributes the 2DEG of two channels and makes lower heterojunction a better carrier confinement which would finally improves the mobility. The best Si doping concentration we have got is 5×1018cm-3, and under this condition, the concentration of the dislocation is 1.6164×109cm-2, surface roughness is 0.210 nm, the mobility is 1754cm2/V·s, the desity of the carrier is 1.25×1013cm-2.3. The decade channels Al Ga N/Ga N heterojunction structures with no Al N insert layer and Al component mutation are grown. The results indicate that the more channel layers, the better surface morphology. The satellite peak in XRD scan curve of ten channels Al Ga N/Ga N heterostructure illustrates the quite good crystalline quality. But with the increase of the channel layer, the electrical properties gets worse, the possible reasons are interface roughness and the uneven relaxation. The same as the double channel Al Ga N/Ga N heterojunction structure, multi-channel impact the strain of barrier layers. The influence of multi-channel Al Ga N/Ga N heterojunction structure on threading dislocation is analysed using TEM, and it shows that the the edge dislocation and the screw dislocation whose directions is perpendicular to the heterojunction can be annihilated, and the dislocationd with other directions can be changed its directions. This can be explained that the surface morphology become better with more channels.In short, the dual-channel Al Ga N/Ga N heterostructures can re- allocate the two-channel modulation 2DEG by doping in the lower barrier layer, and improve the carrier confinement in the lower heterostructures obtaining higher mobility and better electrical characteristics. Multi-channel Al Ga N/Ga N heterojunction structure impact the strain in the barrier layers. And it shows that the the edge dislocation and the screw dislocation whose direction is perpendicular to the multi-channel Al Ga N/Ga N heterojunction can be annihilated, and the dislocationd with other directions can be changed its directions.