GaN/SiO2 interface that does not create states within the band gap: A theoretical prediction

Kengo Nishio,Takehide Miyazaki,Mitsuaki Shimizu

doi:10.1103/physrevmaterials.5.104601

Kengo Nishio, Takehide Miyazaki + Show 1 more

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https://doi.org/10.1103/physrevmaterials.5.104601

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Abstract

For the application of GaN to power transistors, we theoretically search for the interface between GaN and amorphous ${\mathrm{SiO}}_{2}$ $(a\text{\ensuremath{-}}{\mathrm{SiO}}_{2})$ that meets the following requirements: (1) both the conduction band minimum and valence band maximum originate from the GaN (straddling band gap) and (2) the formation of states in the band gap of the GaN is minimized. To this end, we first show that an epitaxial silica bilayer on $m$-plane GaN $(m\text{\ensuremath{-}}\mathrm{GaN})$ meets these requirements when the GaN surface is doped with zinc and oxygen. By using this epitaxial layer as a seed, we make a structure model of the $m\text{\ensuremath{-}}\mathrm{GaN}/a\text{\ensuremath{-}}{\mathrm{SiO}}_{2}$ interface with a straddling gap without in-gap states. Our findings show that a key determinant of the nature of $m\text{\ensuremath{-}}\mathrm{GaN}/a\text{\ensuremath{-}}{\mathrm{SiO}}_{2}$ interface band structure is what we call the ``contact structure,'' a region of just a few atomic layers thickness at the very interface. We propose that the complex problem of designing semiconductor/insulator interfaces can be reduced to the simpler problem of designing ultrathin epitaxial insulators on the semiconductor surface.

Highlights

Interfaces between different materials are ubiquitous, and their atomic structure has been a major subject of materials science [1,2,3]
In this work, using first principles calculations and classical molecular dynamics simulations, we search for the m-plane gallium nitride (GaN) (m-GaN)/aSiO2 interface that meets the following requirements: (1) both conduction band minimum (CBM) and valence band maximum (VBM) originate from the GaN and (2) no states form in the band gap of the GaN
For the application of GaN to power transistors, the interface between GaN and the gate insulator needs to meet the following requirements: (1) both CBM and VBM originate from the GaN and (2) the formation of in-gap states is minimized

Summary

Introduction

Interfaces between different materials are ubiquitous, and their atomic structure has been a major subject of materials science [1,2,3]. In metal-oxide-semiconductor field-effect transistors, a gate insulator is grown on a semiconductor surface [4]. Since the semiconductor and insulator have different atomic structure, dangling bonds are formed at the semiconductor/insulator interface. Such defects need to be reduced, for they create electronic states in the band gap, which degrade the performance of transistors [5]. Amorphous silica (a-SiO2) is often used as the gate insulator in GaN-based transistors [7,8,9]. An experimental study has suggested that the GaN/a-SiO2 interface has more dangling bond states near the valence band maximum (VBM) than the conduction band minimum (CBM) [10]. The reduction of dangling bond states, ones near VBM in particular, is a challenge for the application of GaN

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