A Study On The Characterics Of Superlattice-AlGaN Channel Heterostructure

In order to meet the needs for high frequency, wide bandgap, high power characteristics of wireless communication, radar and other applications devices,from the early ninety’s of the twentieth century, people has turned researchs from electronic compound semiconductor devices to the wide band gap semiconductor devices. Since 1970 s, the researchs on Ga N has undergone a more than 40 years’ rapid development period.After lots of scientitists’ personnel efforts on the Ga N research, Ga N finally applied to the market and is developing step by step to higher performance. Since 1993, Ga N blue light emitting diodes was commercially used, the optoelectronic devices have become the mainstream of the Ga N application. Since the Al Ga N/Ga N heterostructure can form a two dimensional electron gas(2DEG) with a density of over 1×1013cm-2even without being doped, the Al Ga N/Ga N heterojunction HEMTs have a brilliant prospects.People usually focus on the reasearch on the materials and its HEMT devices of Al Ga N/Ga N heterojunction. With the development of the growth techniques and its mechanism of Al Ga N/Ga N heterojunction, it is becoming more and more diversified,such as the double heterojunction structures and the double / multi-channels heterojunction structures can also improve the electrical properties of the heterojunctions, providing spaces for the development of high power microwave devices. Due to the breakdown field of Al N is 3 times bigger than that of Ga N, so we consider to use Al Ga N layer as channel layer of the heterostructures to improve its breakdown voltage. Studies of recent years have confirmed that Al Ga N layer used as the channel layer can indeed increase the breakdown voltage of the HEMTs. For the,The international experts have done a lot of researchs on growth process of Al Ga N channel heterostructure and ways to improve its characteristics and made a great progress. This paper studied the growth of Al Ga N channel heterojunctions on sapphire substrates with different structures on the support of the wide bandgap semiconductor laboratory with the use of MOCVD320 equipment and other testing equipments. The main works are as follows:1. Use the MOCVD device to grow Al Ga N channel heterostructures of 18% Al composition with the direct growth of Al Ga N buffer layer, composite graded Al composition of Al Ga N buffer layer and graded Al component of the Al Ga N bufferlayer with equal thickness. Based on the analysis of sample test results, we could find out that Al Ga N channel heterostructures of 18% Al composition with the direct growth of Al Ga N buffer layer and the graded Al component of the Al Ga N buffer layer with equal thickness have a better electrical performance.2. Use the MOCVD equipment to grow Al Ga N channel heterostructures of 33% Al composition with single composition directly growth of Al Ga N buffer layer, composite graded Al composition of Al Ga N buffer layer. The study indicated that Al Ga N channel heterostructures of 33% Al composition with composite graded Al composition of Al Ga N buffer layer could improve the crystalline quality of materials, increase its mobility and reduce the sheet resistance.3. On the basis of the study on using the Ga N/Al N superlattice structure instead of alloy Al Ga N as the barrier layer to improve the quality of the heterojunction material, try to grow Ga N/Al N superlattice structure as the Al Ga N channel layer. We also used MOCVD equipment to grow superlattice Al Ga N channel heterojunction on the sapphire substrate of 33% Al composition with graded Al composition of Al Ga N buffer layer.The results showed that the introduction of Ga N/Al N superlattice structure can effectively reduce the defects in the materials, improve the 2DEG mobility and reduce the sheet resistance. It meant that the introduction of the Ga N/Al N superlattice structure is a good way to improve the material quality.4. Based on the research in the previous section, we continued to study the superlattice Al Ga N channel heterojunction of 33% Al composition and found out that the dislocation density in the materials reduce about half, 2DEG mobility increased from844cm2/V·s to 1099 cm2/V·s and the sheet resistance decreased from 1528 Ω/□ to736Ω/□. So we could conclude that there is a very significant improvement on material properties.