Systematic Study of Insulator Deposition Effect (Si₃N₄, SiO₂, AlN, and Al₂O₃) on Electrical Properties in AlGaN/GaN Heterostructures

Abstract

To systematically examine the effect of insulator deposition on the electrical properties in AlGaN/GaN heterostructures, the Si- and Al-based insulators (Si3N4, SiO2, AlN, and Al2O3) have been deposited on Al0.3Ga0.7N/GaN heterostructures. A significant increase in two-dimensional electron gas (2DEG) density (Ns) was observed for all the insulators with the order of Ns(Al2O3) > Ns(AlN) ∼ Ns(SiO2) > Ns(Si3N4) > N0 (N0: Ns without insulators). This resulted in a decrease in sheet resistance (R) with the smallest order of R(Al2O3) < R(AlN) < R(Si3N4) < R0 ∼ R(SiO2) (R0: R without insulators). This order is the same as that of Ns except for SiO2, where the 2DEG mobility largely degraded due to the diffusion of Si atoms into nitride layers. The increase in Ns was theoretically analyzed in terms of the change in the potential profile, and the following parameters were extracted: (i) the surface potential barrier (φB), and (ii) the interface charge (NInt) between an insulator and AlGaN. φB (eV) was estimated to be 1.7 (Si3N4), 2.2 (AlN), 2.7 (Al2O3), and 3.6 (SiO2), exhibiting a positive correlation between φB and the bandgap of the insulator. NInt (1013 cm-2) was estimated to be ∼0 (Si3N4), 0.1 (SiO2), 0.3 (AlN), and 0.5 (Al2O3); thus, the interface was found to be positively charged for AlN and Al2O3, whereas it was found to be almost neutral for Si3N4 and SiO2. Thus, the insulator deposition effect has been shown to be significant and to vary among insulators. The analysis shown here offers a guideline for understanding and designing the electrical properties in AlGaN/GaN heterostructures, where insulators are deposited as surface passivation and/or gate insulators.

Temperature-Dependent Interface-State Response in an Al2O3/n-GaN Structure

“…Faster responses with larger magnitudes also appeared in the time-dependent capacitance at high temperatures. From a simple analysis of the C-t results, we estimated the capture cross section of the states to be on the order of 10 -19 cm 2 .KEYWORDS: GaN, MIS, interface state, C-V, C-t, high temperature, capture cross section *E-mail address: hashi@rciqe.hokudai.ac.jpAn insulated-gate structure is very attractive for GaN-based high-efficiency power switching devices and high-power transistors operating at high frequency [1][2][3]. For realization of well-controlled and reliable insulated-gate structure, it is necessary to achieve an insulator-semiconductor (I-S) interface with a low density of electronic states [1,4,5].…”

Threshold voltage control using SiNx in normally off AlGaN/GaN HFET with p‐GaN gate

“…Ti/Al/Ti/Au was used as the source-drain electrode. As the gate insulator, we used SiN x because SiN x shows a low interface trap density when it is used for surface passivation [7]. The p-GaN layer was etched away by RIE except for the gate region to expose surface of AlGaN barrier.…”

“…Although there are several disadvantages, the most important advantage of using a MIS structure with p-GaN gate is that we can control threshold voltage for high-power application. In this study, we used SiN x as an insulator to control the V th of the JHFET and also as a passivation layer of the surface except for the gate region [7].…”

Controlling the interface charge density in GaN-based metal-oxide-semiconductor heterostructures by plasma oxidation of metal layers

“…As boundary condition, it is assumed that the increase in barrier height for a MOS structure compared to a Schottky-gated structure is fully compensated by the additional conduction band offset between oxide and barrier. This assumption appears arbitrary, however, even assuming reasonable variations in the order of 0.3 eV, 22 the resulting change in N it would only be about 10%. On the basis of the Schottky sample, parameters for U B and r int have been extracted to be 1.36 eV and 1.53 lC/cm 2 , respectively.…”