Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors
- 1 July 2003
- journal article
- Published by American Vacuum Society in Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
- Vol. 21 (4), 1844-1855
- https://doi.org/10.1116/1.1589520
Abstract
In order to clarify the mechanisms of drain current collapse and gate leakage currents in the AlGaN/GaN heterostructure field effect transistor (HFET), detailed electrical properties of the ungated portion and Schottky-gated portion of the device were investigated separately, using a gateless HFET structure and an AlGaN Schottky diode structure. The gateless device was subjected to plasma treatments and surface passivation processes including our novel Al2O3-based surface passivation. dc I–V curves of gateless HFETs were highly nonlinear due to virtual gating by surface states. After drain stress, air-exposed, H2 plasma-treated and SiO2-deposited gateless HFETs showed an initial large-amplitude exponential current transient followed by a subsequent smaller, slow, and highly nonexponential response. The former was explained by emission from deep donors at Ec–0.37 eV, and the latter by emission from surface states. Capture transients with stress-dependent capture barriers were also observed. An x-ray photoelectron spectroscopy (XPS) study indicated that 0.37 eV-deep donors are N-vacancy related. On the other hand, no current transients took place in N2 plasma treated and Al2O3-passivated samples. Temperature dependences of I–V curves of Schottky diodes were extremely small and reverse currents were anomalously large. They were explained by the "thin surface barrier" (TSB) model where thermionic field emission and field emission through the TSB region formed by deep donors produce leakage current paths. By combining the results on gateless HFETs and Schottky diodes, a new unified model of near-surface electronic states for the free surface and Schottky interface of AlGaN is proposed. It consists of a U-shaped surface state continuum and N-vacancy related near-surface discrete deep donors. The model can explain the observed large gate leakage and drain current collapse in AlGaN/GaN HFETs in a unified way. It is also shown that our novel Al2O3 passivation, when also used as a gate insulator, can completely suppress current collapse and gate leakageKeywords
This publication has 29 references indexed in Scilit:
- Current Collapse in AlGaN/GaN HEMTs Investigated by Electrical and Optical Characterizationsphysica status solidi (a), 2002
- Influence of MgO and Sc2O3 passivation on AlGaN/GaN high-electron-mobility transistorsApplied Physics Letters, 2002
- Si 3 N 4 / AlGaN/GaN –metal–insulator–semiconductor heterostructure field–effect transistorsApplied Physics Letters, 2001
- The impact of surface states on the DC and RF characteristics of AlGaN/GaN HFETsIEEE Transactions on Electron Devices, 2001
- Lateral AlxGa1−xN power rectifiers with 9.7 kV reverse breakdown voltageApplied Physics Letters, 2001
- Highly doped thin-channel GaN-metal–semiconductor field-effect transistorsApplied Physics Letters, 2001
- Microwave Performance of 0.3-µm Gate-Length Multi-Finger AlGaN/GaN Heterojunction FETs with Minimized Current CollapseJapanese Journal of Applied Physics, 2000
- High performance microwave power GaN/AlGaN MODFETs grown by RF-assisted MBEElectronics Letters, 2000
- High-power microwave GaN/AlGaN HEMTs on semi-insulating silicon carbide substratesIEEE Electron Device Letters, 1999
- Short-channel Al0.5Ga0.5N/GaN MODFETs with power density > 3 W/mm at 18 GHzElectronics Letters, 1997