Study of the n+ GaN cap in AlGaN/GaN high electron mobility transistors with reduced source-drain resistance

An n(+) GaN cap layer has been applied on an AlGaN/GaN high electron mobility transistor (HEMT) to achieve a non-alloyed ohmic contact. Delta dopings were used at the heterointerface of the n(+) GaN cap and AlGaN layer to lower the AlGaN potential barrier and to improve communication between the n+ GaN cap and the two-dimensional electron gas (2DEG) channel. Non-alloyed ohmic contact resistance as low as 0.2 Omega-mm, and sheet resistance of 60 Omega/square were achieved. Selective etch and sidewall technology were applied during processing. The n(+) capped device was fabricated and compared to a standard AlGaN/GaN HEMT. Lower on-resistance and access resistance, higher f(tau), and f(MAX), and better linearity in terms of were achieved.