Growth Of AlInN/GaN Heterostructure And Electronic Characteristics Of Double-Channel HEMT

III-V nitride materials, as the promising materials for third generation semiconductors, have been widely studied in optoelectronics and microelectronics. Among the III-V nitride materials, Al1-xInxN alloy is well known for its potentialities, that it can be grown perfectively lattice-matched (LM) to GaN as an indium content close to 0.16⁰.18. LM AlInN has demonstrated outstanding advantages in high electron mobility transistor (HEMT). AlInN HEMTs have attracted increasing interest, due to no residual stress, high spontaneous polarization difference and high stability. However, the AlInN/GaN HEMT still has some issues to prevent its application, such as low electron mobility and device linear. Additionally, the high crystalline quality LM AlInN materials are easily influenced by compositional homogeneities, due to the large mismatch existing between InN and AlN covalent bonds. In this work, in order to solve these issues, growth mechanism of vertical compositional imhomogeneities and optimization of the crystalline quality of the LM AlInN films were investigated. Additionally, a novel AlInN/GaN HEMT device structure was designed and the electronic and I-V characteristics of this device were investigated. These studies paved the way to improving the electronic characteristics of the AlInN/GaN HEMT.Firstly, the growth mechanism of vertical imhomogenities in the AlInN films grown by metalorganic chemical vapor deposition (MOCVD) on GaN substrates was studied. Some self-organized metallic In droplets with uniform size could be formed during the imhomogenous AlInN material growth by MOCVD, when the In was excess caused by initial rich-Al AlInN film. The In droplets increased the surface transient In contents. The variation of the In droplet density with thickness resulted in the In fraction fluctuation along the growth direction. As a result, the vertical In imhomogenities of the AlInN films grown by MOCVD was attributed to the In droplets.In order to fabricate homogeneity LM AlInN/GaN film, the influences of growth parameters on the In droplets and the AlInN crystalline quality were investigated. The In droplets could be eliminated by reducing the AlInN film growth rate. The increases of the hydrogen flux and the growth temperature could reduce the In absorption efficiency. Meanwhile, the growth rate was decreased by increasing the V/III, resulting in a reduction of the In absorption efficiency. With the deviation of the In fraction from 0.18, the surface roughness and the dislocation density of the AlInN films were increased. Finally, after optimization of the growth parameters, the high crystalline quality LM AlInN films could be deposited at 790 oC, with V/III (NH3:TMAl:TMIn) equal to 500:20:200.Based on the theoretical calculation of the electron transportation in AlInN/GaN heterstructure, a novel double-channel AlInN/GaN heterostrcuture was designed. This structure had a high electron mobility, a low sheet resistance and a high uniform sheet resistance. In the AlInN/GaN heterostrcuture, the room temperature (RT) electron mobility was predominantly limited by interface roughness and polar optical phonon scattering, which were increased with the sheet density. The electron mobility could be enhanced by reducing the sheet density. In order to improve the electron mobility and keep the 2DEG sheet density unchanged, a novel double-channel (D-C) HEMT was designed. The D-C AlInN/GaN HEMT structure was realized by inserting an AlN/GaN/AlN quantum well between AlInN and GaN layer. In this D-C HEMT, the 2DEG was confined in the two channels (top and bottom), and the electron mobility was increased by reducing the sheet density in the both channels. As a result, the D-C AlInN/GaN heterostructure has high electron mobility and low sheet resistance properties. It was found that the interface roughness as a key factor influenced the uniformity of the sheet resistance in the single-channel (S-C) heterostructure. Whereas, by modifying the 2DEG distribution along the growth direction, the high uniformity of the sheet resistance was realized in the D-C AlInN/GaN heterostructure. After structure optimization, in the D-C AlInN/GaN HEMT the electron mobility could be enhanced to 1570 cm2/Vs, and the sheet resistance and its nonuniformity could be reduced to 222 ?/sq and 0.7 %, respectively.The new D-C AlInN/GaN HEMT was fabricated by using the above growth technologies. By considering the device simulation and experiment results, the I-V output characteristics were investigated. The simulation results showed the D-C AlInN/GaN HEMT had good gate control ability. Between the top and bottom channel in the D-C HEMT, the top channel 2DEG demonstrated better gate control. To compare with the S-C AlInN/GaN HEMT, the D-C AlInN/GaN HEMT had two extreme points of the transconductance and a large pinch-off voltage. The experimental results showed that the maximum saturated output current was 980 mA/mm at V_GS=5V. The pinch-off voltage was -6.2 V, in the D-C AlInN/GaN HEMT. The D-C AlInN/GaN HEMT demonstrated good gate control ability, and two extreme points of the transconductance at -4V and -2V. Additionally, in the unmpassivated D-C AlInN/GaN HEMT, the I-V output current demonstrated an obviously current collapse under the large bias of gate and drain. It was found that the output current of the top channel showed more severe current collapse than the bottom channel, due to the influence of the surface traps.In summary, based on the high crystalline quality LM AlInN/GaN films, a novel D-C AlInN/GaN HEMT was designed and fabricated. And the characteristics of the electron mobility and the device linear were both improved in the D-C AlInN/GaN HEMT, and the corresponding issues of the S-C AlInN/GaN HEMT were solved in this device.