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

Abstract

Two surface treatments of GaN, prior to atomic layer deposition (ALD) of Al 2 O 3 , were compared to investigate electronic and chemical interface properties: (1) HCl followed by HF and (2) NH 4 OH. Constant capacitance deep level transient and optical spectroscopies (CC-DLTS/CC-DLOS) and X-ray photoelectron spectroscopy (XPS) were used to study the impact of the surface treatments on the interface state density (D it ) and the chemical composition of the Al 2 O 3 /GaN interface, respectively. It was determined that the HCl/HF treatment resulted in 3-10 times higher D it near the GaN conduction band, while the NH 4 OH treatment resulted in nearly 10 times higher D it deeper in the GaN bandgap. XPS revealed that the HCl/HF treatment left residual adsorbed fluorine atoms at the interface and that the NH 4 OH treatment resulted in a higher concentration of carbon near the Al 2 O 3 /GaN interface. These results are discussed in relation to the relevant literature in attempt to understand the relationship between the chemical composition at the interface and the observed differences in D GaN metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) are typically used for power electronics applications, and being considered for highly-scaled and enhancementmode operation in radio-frequency (RF) applications. In these applications, a metal-insulator-semiconductor (MIS) device structure can result in decreased gate leakage current and higher breakdown voltages versus the traditional Schottky-based HEMT structure. However, the insulator-semiconductor interface can lead to high concentrations of interface states that can negatively affect device performance and reliability.1-3 Thus, various groups have focused on improving possible gate dielectrics to reduce surface states and decrease gate leakage while maintaining small equivalent oxide thicknesses. Al 2 O 3 has, in particular, received much attention as a possible gate dielectric because of its potential to provide low leakage and low interface state densities. [4][5][6][7] Nonetheless, prior work indicates that the initial conditions of the GaN surface can significantly influence the quality of the resultant interface.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; 9-13 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.12 However, reports have conflicted regarding which of these two results in lower carbon concentration. 13,16 In the broader GaN-related literatu...

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Influence of environmental conditions and surface treatments on the photoluminescence properties of GaN nanowires and nanofins

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Impact of NaOH solution surface treatment on Al2O3/β-Ga2O3 MOS capacitors

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