Interface Trap Density Reduction for Al₂O₃/GaN (0001) Interfaces by Oxidizing Surface Preparation prior to Atomic Layer Deposition

Abstract

We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

“…The device output curves are shown in Figure d exhibiting good saturation characteristics and R on value of 31.5 mΩ cm 2 with a gate width of 100 µm (50 µm × 2; see the Supporting Information). The modest hysteresis observed in the transfer curves (Figure S13, Supporting Information) and the relatively high R on observed for these first vertical GaN‐on‐Si trench MOSFETs can be further optimized with gate surface treatments and regrowth, and with engineering the doping profile in the drift layers . Additional work is also required for device edge termination in order to achieve high breakdown voltages in these devices.…”

Interface formation of Al2O3 on n‐GaN(0001): Photoelectron spectroscopy studies

“…Physical vapor deposition (PVD) is successfully used for the growth of the aluminum oxide 39–41 on other substrates, and it seems like an interesting choice for an alternative to ALD‐Al 2 O 3 . Al 2 O 3 /n‐GaN system is widely studied by many groups, 3,42–48 mostly focusing on near interface trap density and electrical properties. So far, a few reports have been published on the properties of the Al 2 O 3 /n‐GaN interface formed by ALD 12,18,49 but none by PVD.…”

Impact of Surface Treatment on Interface States of ALD Al2O3/GaN Interfaces

“…15,16 Of particular concern in these studies, was removal of oxides and organics from the surface. A 1999 study by Koyama et al compared a combined HCl and HF treatment to a NH 4 OH treatment using XPS, showing that both treatments resulted in oxide removal.…”

“…13,16 In the broader GaN-related literature, there is still little consensus about the optimal GaN surface treatment. Yun et al report using a H 2 SO 4 :H 2 O 2 treatment followed by HCl.…”

“…8 Processes to clean the GaN surface have been a topic of research for the last two decades, although early studies primarily focused on preparing the surface for metallization; [9][10][11][12][13] this extensive work was well summarized by Long et al 14 More recently, the topic of surface treatment before dielectric deposition has become a topic of interest, as the search for optimal dielectric materials for use with the GaN material system has grown. 15,16 Of particular concern in these studies, was removal of oxides and organics from the surface. A 1999 study by Koyama et al compared a combined HCl and HF treatment to a NH 4 OH treatment using XPS, showing that both treatments resulted in oxide removal.…”