Charge Storage Mechanism of Drain Induced Dynamic Threshold Voltage Shift in ${p}$ -GaN Gate HEMTs.

The drain induced dynamic threshold voltage (${V}_{\textrm {th}}$) shift of a ${p}$ -GaN gate HEMT with a Schottky gate contact is investigated, and the underlying mechanisms are explained with a charge storage model. When the device experiences a high drain bias ${V}_{\textrm {DSQ}}$ , the gate-to-drain capacitance (${C}_{\textrm {GD}}$) is charged to ${Q}_{\textrm {GD}}$ (${V}_{\textrm {DSQ}}$). As the drain voltage drops to ${V}_{\textrm {DSM}}$ where ${V}_{\textrm {th}}$ is measured, ${C}_{\textrm {GD}}$ is expected to be discharged to ${Q}_{\textrm {GD}}$ (${V}_{\textrm {DSM}}$). However, the metal/ ${p}$ -GaN Schottky junction could block the discharging current, resulting in storage of negative charges in the ${p}$ -GaN layer. For the device to turn on, additional gate voltage is required to counteract the stored negative charges, resulting in a positive shift of ${V}_{\textrm {th}}$. The dynamic ${V}_{\textrm {th}}$ shift is an intrinsic and predictable characteristic of the ${p}$ -GaN gate HEMT which is linearly correlated with $\Delta \!{Q}_{\textrm {GD}}={Q}_{\textrm {GD}}$ (${V}_{\textrm {DSQ}}$) $- {Q}_{\textrm {GD}}$ (${V}_{\textrm {DSM}}$). The ${V}_{\textrm {th}}$ shift is dependent on ${V}_{\textrm {DSQ}}$ as well as ${V}_{\textrm {DSM}}$ , indicating that the ${V}_{\textrm {th}}$ shift is varying along the load line during a switching operation. [ABSTRACT FROM AUTHOR]