Study On Growth Of GaN-Based HEMT Materials With High-Resistance Buffer Layer And High Mobility

Gallium Nitride (GaN), the representative of the third-generation compound semiconductor materials, owing to its high breakdown field, good thermal conductivity, corrosion resistance, and radiation hardness, had been known as the ideal material for the development of microwave power devices. In recent years, with the improving of the GaN epitaxial equipment, the crystalline quality of GaN material increasing gradually, coupled with the maturity of the device manufacturing process, the performance of AlGaN/GaN high electron mobility transistors had been able to meet the needs of the defense electronics and communication applications fields. There are two issues of concern in the traditional hetero-junction, one is the high resistivity of GaN buffer layer, and another is the optimized hetero-structure. Both of them are related wity the device operating characteristics closely.Firstly, this paper starting from the studies of the impurities distribution in GaN buffer layer, the current leakage of buffer layer can be divided into two cases. One is the buried layers which have gathered high concentration of carriers, and another is background carriers which have distributed throughout the GaN buffer layer. After the optimized growth conditions have been used in high-temperature AlN (HT-AlN) nucleation layer, we have controlled the spread of oxygen impurities in the 3D nucleation islands and the background carriers'concentration also have been controlled in the order of 1014cm-3. However, at the GaN-based microwave power device is working, the junction temperature always more than 150 degrees. In this case, a large number of electrons will be intrinsic inspired in the GaN buffer layer. In addition, a large number of two-dimensional electrons located in the channel will overflow to the GaN buffer layer when the GaN-based device working in the negative gate voltage. These would seriously effect on the impedance characteristics of GaN buffer layer. At this time, we need to bind these background carriers by deep level traps which through the appropriate amount of Fe doping in the GaN buffer layer. Only this way can ensure the impedance characteristics of buffer layer at the GaN-based microwave power devices working.Secondly, we have researched the most optimized structure of conventional AlGaN/GaN hetero-structure. By analyzing the impact of the multiple scattering mechanisms existed in GaN material to the 2DEG transport properties of AlGaN/GaN channel. Combined with the test results of our samples, we have optimized the AlN interlayer, AlGaN barrier layer and GaN cap layer.Third, as polar semiconductor material, the 2DEG density at the GaN channel is directly related to the strain of AlGaN barrier layer. But the residual stress at the GaN epitaxial layer is extremely unfavorable to the reliability of device. Affected by the inverse piezoelectric effect, the GaN-based devices which existed residual stress will lead to be damaged and could not be repaired.Last, in order to reduce costs and improve material utilization, the diameter of GaN wafer will be increasing inevitably. In our laboratory, we had implemented high quality GaN films growing on 3, 4 inch sapphire and Sillcon Carbon substrates, and the entire wafer had a better uniformity. The AlGaN/GaN hetero-structure also had been grown on these templates, which electrical characteristics and uniformity are also able to meet the needs of the device manufacturing.