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Sodium beta-alumina(SBA) is deposited on AlGaN/GaN by using a co-deposition process with sodium and Al_2O_3 as the precursors.The X-ray diffraction(XRD) spectrum reveals that the deposited thin film is amorphous.The binding energy and composition of the deposited thin film,obtained from the X-ray photoelectron spectroscopy(XPS) measurement,are consistent with those of SBA.The dielectric constant of the SBA thin film is about 50.Each of the capacitance-voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and AlGaN.The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor(MISHEMT) is measured to be(3.5～9.5)×10~(10) cm~(-2)·eV~(-1) by the conductance method.The fixed charge density of SBA dielectric is on the order of 2.7×10~(12) cm~(-2).Compared with the AlGaN/GaN metal-semiconductor heterostructure high-electronmobility transistor(MESHEMT),the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively. However,the threshold voltage of the AlGaN/GaN MISHEMT using SBA as the gate dielectric shifts positively from—5.5 V to—3.5 V.From XPS results,the surface valence-band maximum(VBM-E_F) of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition.The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum (VBM-E_F),the reduction of interface traps and the effects of sodium ions,and/or the fixed charges in SBA on the two-dimensional electron gas(2DEG).
Sodium beta-alumina (SBA) is deposited on AlGaN / GaN by using a co-deposition process with sodium and Al 2 O 3 as the precursors. X-ray diffraction (XRD) spectrum reveals that the deposited thin film is amorphous. Binding energy and composition of the deposited thin film, obtained from the X-ray photoelectron spectroscopy (XPS) measurement, are consistent with those of SBA. The dielectric constant of the SBA thin film is about 50. Each of the capacitance-voltage characteristics obtained at five different The frequencies of a high-quality interface between SBA and AlGaN.The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor (MISHEMT) is measured to be (3.5~9.5) × 10~10 cm ~ (- 2) · eV -1 (-1) by the conductance method.The fixed charge density of SBA dielectric is on the order of 2.7 × 10 ~ (12) cm -2 .Compared with the AlGaN / GaN metal-semiconductor heterostructure high-electronmobility transistor (MESHEMT), the AlGaN / GaN MISHEMT usually has a threshold voltage t hat shifts negatively. However, the threshold voltage of the AlGaN / GaN MISHEMT using SBA as the gate dielectric shifts positively from-5.5 V to-3.5 V. From XPS results, the surface valence-band maximum (VBM-E_F) of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition. These possible reasons why the threshold voltage of AlGaN / GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence- band maximum (VBM-E_F ), the reduction of interface traps and the effects of sodium ions, and / or the fixed charges in SBA on the two-dimensional electron gas (2DEG).