The Fabrication And Contact Characteristics Of AlGaN/GaN HEMT

GaN based material have a huge advantage in high frequency, high power, radiation, high temperature conditions because of its large band gap, high saturated electron velocity, high breakdown electric field and has good corrosion resistance, radiation resistance and high thermal conductivity. Due to the inside of the Al GaN / GaN HEMT exist strong spontaneous polarization and piezoelectric polarization makes the Al GaN / GaN heterojunction can spontaneously form rate two-dimensional electron gas with high concentration and high electron mobility, has now become the focus of research at home and abroad. Due to the large band gap of GaN and Al GaN / GaN HEMT is unintentionally doped epitaxial material, which makes the formation of a small ohmic contact resistance is difficult. However, smaller ohmic contact resistance for high power, high frequency devices plays a vital role. Currently one of the important directions for Al GaN / GaN HEMT devices is how to get good surface morphology, small contact resistance, stable and reliable ohmic contact. In this paper, we studies the key process of HEMT Al GaN/GaN devices, and mainly studies effects of different ohmic contact patterns on the ohmic contact characteristics of HEMT Al GaN/GaN.First,the paper introduces the design ideas of the process layout for the preparation of HEMT, and analyzes the preparation of HEMT process from the aspects of active zone isolation, ohmic electrode preparation and gate preparation.Secondly, in order to study effects of different ohmic contact patterns on the ohmic contact characteristics of HEMT Al GaN/GaN, the experimental scheme of the annealing furnace with slow and multi stage annealing was designed. Experimental results show: 1.Electrode structure with longitudinal contact holes annealed at acceptable temperature range is bigger. That is to say when the annealing temperature around the ideal of annealing temperature fluctuation electrode structure with longitudinal contact holes are more likely to form ohmic contact and experimental data showed that the contact resistance is smaller. 2.Electrode structure with longitudinal contact holes required shorter annealing time and experimental data show that short-term annealing can get a better surface morphology. 3.By layout ICP etch to etch different side of longitudinal contact holes. Experimental data show that ohmic contact resistance with the shorter side of the longitudinal contact holes is small. Which can be inferred metal electrode could not in direct contact with the two-dimensional electron gas, because if the metal electrodes in direct contact with the two-dimensional electron gas then it should be ohmic contact resistance with the larger side of the longitudinal contact holes is small. Because the long side means a larger contact area with two-dimensional electron gas, the resistance should be small. 4. When the gate voltage is small,the transconductance of HEMT device with longitudinal contact holes is larger than the regular HEMT device's transconductance;When the gate voltage is large,the transconductance of HEMT device with longitudinal contact holes is smaller than the regular HEMT device's transconductance.Finally, the ohmic contact patterns with longitudinal contact holes were optimized. The research shows that the rapid annealing in the high purity N2 after the ICP etching source drain electrode is helpful to reduce the ohmic contact resistance.