The current-conduction mechanisms of the as-deposited and annealed at 450°C (Ni/Pt) Schottky contacts on AlInGaN quaternary alloy have been investigated in the temperature range of 80-320 K. The zero-bias barrier height (BH) (Φ B0) and ideality factor (n) of them were evaluated using thermionic emission (TE) theory. The Φ B0 and n values calculated from the I-V characteristics show a strong temperature dependence. Such behavior of Φ B0 and n is attributed to Schottky barrier inhomogeneities. Therefore, both the Φ B0 vs n and Φ B0 vs q/2kT plots were drawn to obtain evidence on the Gaussian distribution (GD) of the barrier height at the metal/semiconductor interface. These plots show two different linear parts at low and intermediate temperatures for as-deposited and annealed Schottky contacts. Thus, the mean value of Φ B0 and standard deviation (σ 0) was calculated from the linear parts of the Φ B0 vs q/kT plots for both samples. The values of the effective Richardson constant (A Ã) and mean BH were obtained from the modified Richardson plots which included the effect of barrier inhomogeneity. These values of Richardson constant and barrier height for as-deposited contacts were found to be 19.9 A cm −2 K −2 and 0.59 eV, respectively, at low temperature, but 43.3 A cm −2 K −2 and 1.32 eV, respectively, at intermediate temperatures. These values of Richardson constant and barrier height for annealed contacts were found to be 19.6 A cm −2 K −2 and 0.37 eV, respectively, at low temperature, but 42.9 A cm −2 K −2 and 1.54 eV, respectively, at intermediate temperatures. It is clear that the value of the Richardson constant obtained for as-deposited and annealed samples by using double-GD for intermediate temperatures is close to the theoretical value of AlInGaN (=44.7 A cm −2 K −2). Therefore, I-V-T characteristics for the as-deposited and annealed Schottky contacts in the temperature range of 80-320 K can be successfully explained based on TE theory with double-GD of the BHs.

A hybrid approach for obtaining normally off high electron mobility transistors (HEMTs) combining fluorine treatment, recess etch techniques, and AlGaN buffer was studied. The effects of process variations (recess etch depth and fluorine treatment duration) and epitaxial differences (AlGaN and carbon doped GaN buffers) on the DC characteristics of the normally off HEMTs were investigated. Two different epitaxial structures and three different process variations were compared. Epitaxial structures prepared with an AlGaN buffer showed a higher threshold voltage (V th = +3.59 V) than those prepared with a GaN buffer (V th = +1.85 V).

contacts were placed on a quaternary Al 0.84 In 0.13 Ga 0.03 N epilayer. The electrical and structural properties of the asdeposited Pt/Au, Ni/Au, Ni/Pt/Au and annealed Ni/Pt/Au Schottky contacts were investigated as a function of annealing temperature using currentvoltage (I-V), capacitance-voltage (C-V), and high resolution x-ray diffraction measurements (HR-XRD). According to the I-V, Norde, and C-V methods, the highest Schottky barrier height (SBH) was obtained for the Pt/Au (0.82 eV (I-V), 0.83 eV (Norde), and 1.09 eV (C-V)) contacts when they were compared with the other as-deposited Schottky contacts. The estimated SBH of the annealed Ni/Pt/Au Schottky contacts, calculated from the I-V results, were 0.80 eV, 0.79 eV, and 0.78 eV at 300°C, 400°C, and 500°C, respectively. The SBH decreases with an increase in the annealing temperature up to 500°C compared with that of the as-deposited Ni/Pt/Au Schottky contact. The observed extra peaks in the annealed samples confirm the formation of a new interfacial phase at the interface. However, the diffraction patterns of the annealed Schottky contacts did not change as a function of the annealing temperature. The higher ideality factors values were obtained for as-deposited Pt/Au (5.69), Ni/Au (6.09), and Ni/Pt/Au (6.42) Schottky contacts and annealed Ni/Pt/Au (6.42) Schottky contacts at 300°C (6.89), 400°C (7.43), and 500°C (8.04). The higher n results can be attributed to current-transport mechanisms other than thermionic emission, such as dislocation related tunneling.

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We demonstrate the electrical performances of an AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) with low gate leakage current (I g ). A low gate leakage current as low as the order of 10 −11 A/mm was achieved from normally-off MIS-HEMT device (V th = 2.16 V) with a partially recessed gate, fluorine treatment, and ALD Al 2 O 3 gate dielectric layer. The gate leakage current decrease is attributed to the pre-treatment of the gate region with hydrofluoric acid (HF) and deionized water (DI) solution, which acts to remove the native oxide layer and thus decrease interface traps. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses demonstrate that the AlGaN surfaces are modified such that the surface roughness and native oxide introduced by the treatments used to achieve normally-off operation are remedied with the use of the pre-treatment.