Defect Structure Determination of GaN Films in GaN/AlN/Si Heterostructures by HR-TEM, XRD, and Slow Positrons Experiments

Vladimir Lucian Ene,Victor Leca,Iulia Zai,Nikolay Djourelov,Bogdan Stefan Vasile,Andreea Bianca Serban,Doru Dinescu,Ecaterina Andronescu

doi:10.3390/nano10020197

Abstract

The present article evaluates, in qualitative and quantitative manners, the characteristics (i.e., thickness of layers, crystal structures, growth orientation, elemental diffusion depths, edge, and screw dislocation densities), within two GaN/AlN/Si heterostructures, that alter their efficiencies as positron moderators. The structure of the GaN film, AlN buffer layer, substrate, and their growth relationships were determined through high-resolution transmission electron microscopy (HR-TEM). Data resulting from high-resolution X-ray diffraction (HR-XRD) was mathematically modeled to extract dislocation densities and correlation lengths in the GaN film. Positron depth profiling was evaluated through an experimental Doppler broadening spectroscopy (DBS) study, in order to quantify the effective positron diffusion length. The differences in values for both edge and screw dislocation densities, and correlation lengths (Le, Ls) found in the 690 nm GaN film, were associated with the better effective positron diffusion length (Leff) of = 43 ± 6 nm.

Highlights

Binary semiconductors, such as InN, AlN, GaAs, InAs, InP, GaN, AlSb, etc., and their alloys, cover an extended range of structures useful in high-end device technology [1,2]
The lattice mismatch between GaN and Si (1121) is lower (16.9%) than in the case of AlN and Si (1121) (18.9%), the use of an AlN buffer layer is still recommended due to the low mismatch between AlN and GaN (2.4%) that can lead to a lower amount of defects in the final GaN film [24]
Two commercially available GaN/AlN/Si wafers were characterized by means of TEM and XRD in order to assess the relationship of the heterostructures characteristics with the positron diffusion depths, evaluated by Doppler broadening spectroscopy (DBS) studies

Summary

Introduction

Binary semiconductors, such as InN, AlN, GaAs, InAs, InP, GaN, AlSb, etc., and their alloys, cover an extended range of structures useful in high-end device technology [1,2]. Many binary compounds exhibit a very low electron effective mass, a high mobility, which makes them ideal candidates for developing high-speed devices [3]. Among these compounds, GaN has shown impressive advantages. A second advantage is the high mobility (>1200 cm V−1 s−1) of the two-dimensional electron gas (formed at interfaces with e.g., AlN) that leads to low channel resistance and high current density (>1 A mm−1), and a breakdown field of 3.3 MV cm−1 that is 11 times higher than that of silicon (0.3 MV cm−1) [4,5]. The fabrication of defect-free GaN films still possesses interest in some fields, such as field assisted positron moderation [10]

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