Spontaneous and piezoelectric polarization charge effects on contact resistance in AlGaN/GaN HEMT structures

摘要

Ohmic contact resistance in AlGaN/GaN HEMT structures was investigated by using thermionic emission and tunneling theories. It was found that the spontaneous and piezoelectric polarization charges at a heterojunction effectively lower the specific contact resistance of ohmic electrodes. The lowering effect is enhanced at a thin AlGaN, and therefore, the calculated resistance for Ti contact to Al{sub}0.3Ga{sub}0.7N decreased from 53 Ωcm{sup}2 at a thickness of 30 nm to 5.5×10{sup}(-6) Ωcm{sup}2 at 2 nm when the donor concentration was 10{sup}18 cm{sup}(-3). This analysis indicated that the control of AlGaN thickness under the ohmic electrodes is one useful way to lower the contact resistance.