An Actively-Passivated p-GaN Gate HEMT With Screening Effect Against Surface Traps
Yanlin Wu, Jin Wei, Maojun Wang, Muqin Nuo, Junjie Yang, Wei Lin, Zheyang Zheng, Li Zhang, Mengyuan Hua, Xuelin Yang, Yilong Hao, Kevin J. Chen, Bo Shen
Abstract
An active-passivation p-GaN gate HEMT (AP-HEMT), featuring an active p-GaN passivation layer extending into the drain-side access region, is demonstrated on a commercial E-mode p-GaN/AlGaN/GaN heterostructure wafer. The active passivation layer (APL) is electrically connected to the p-GaN gate, and thus can supply/release mobile holes through gate electrode. The mobile holes in the APL effectively shields the overlaying surface traps from depleting the underlying 2DEG channel, and thus results in a much improved dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> . After a 10-ms 650-V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> stress, the measured dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> /static <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> is 4.30 for Conv-HEMT, but only 1.39 for AP-HEMT. Specially designed HEMTs with a surface testing electrode (ST) in the access region are fabricated to verify the screening effect. A negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ST}}$ </tex-math></inline-formula> mimics the virtual gate effect caused by negative surface charges, resulting in a reduced drain current in conventional HEMT (Conv-HEMT). In the AP-HEMT, a negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ST}}$ </tex-math></inline-formula> is shown to induce no change in the drain current, indicating an effective screening of the trap states. On the other hand, under a positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ST}}$ </tex-math></inline-formula> stress applied to a Conv-HEMT, electrons in the 2DEG channel are pulled over the AlGaN barrier and get trapped at the surface, resulting in a sharply decreased drain current after positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ST}}$ </tex-math></inline-formula> is removed. For the AP-HEMT, the drain current remain unchanged after the positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ST}}$ </tex-math></inline-formula> is removed. The actively passivated HEMT exhibits the highly desired suppression of surface trap induced dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> degradation.