Improved p-type conductivity in Al-rich AlGaN using multidimensional Mg-doped superlattices.

T C Zheng,J Y Kang,D J Cai,J C Li,R Liu,S P Li,W Lin

doi:10.1038/srep21897

T C Zheng, J Y Kang + Show 5 more

Open Access

https://doi.org/10.1038/srep21897

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Journal: Scientific Reports	Publication Date: Feb 24, 2016
Citations: 50	License type: CC BY 4.0

Affiliation: Western Sydney University, Xiamen University

Abstract

A novel multidimensional Mg-doped superlattice (SL) is proposed to enhance vertical hole conductivity in conventional Mg-doped AlGaN SL which generally suffers from large potential barrier for holes. Electronic structure calculations within the first-principle theoretical framework indicate that the densities of states (DOS) of the valence band nearby the Fermi level are more delocalized along the c-axis than that in conventional SL, and the potential barrier significantly decreases. Hole concentration is greatly enhanced in the barrier of multidimensional SL. Detailed comparisons of partial charges and decomposed DOS reveal that the improvement of vertical conductance may be ascribed to the stronger pz hybridization between Mg and N. Based on the theoretical analysis, highly conductive p-type multidimensional Al0.63Ga0.37N/Al0.51Ga0.49N SLs are grown with identified steps via metalorganic vapor-phase epitaxy. The hole concentration reaches up to 3.5 × 1018 cm−3, while the corresponding resistivity reduces to 0.7 Ω cm at room temperature, which is tens times improvement in conductivity compared with that of conventional SLs. High hole concentration can be maintained even at 100 K. High p-type conductivity in Al-rich structural material is an important step for the future design of superior AlGaN-based deep ultraviolet devices.

Highlights

Al-rich (Al > 0.5) AlGaN alloys are a promising class of materials because they are especially suited for realizing deep ultraviolet optoelectronic devices with operating wavelength down to 200 nm[1,2,3,4]
We propose multidimensional SL doping extending in-plane layers of conventional SL doping into higher dimension, which is expected to enhance the vertical hole conductivity
Based on the projected densities of states (DOS) of valence bands along the [0001] direction for each bilayer in Fig. 2, the valence band maximum (VBM) in 3D SL with the largest DOS is located at the interface between well and barrier, similar to conventional SL

Summary

Introduction

Al-rich (Al > 0.5) AlGaN alloys are a promising class of materials because they are especially suited for realizing deep ultraviolet optoelectronic devices with operating wavelength down to 200 nm[1,2,3,4]. Confined parallel sheets of two-dimensional (2D) hole gases are formed in Mg-doped low Al-content AlGaN/GaN SLs26,28 Such parallel 2D hole sheets suffer from low conductivity along the c vertical axis.because of large potential barriers that require the hole to transport through tunneling or thermionic emission processes caused by strong polarization fields and valence band discontinuity[30,31,32,33], they have high in-plane conductivity. Hole scatterings become increasingly significant as Al content increases, which aggravates low vertical hole mobility[34,35,36] In this case, developing an alternative strategy for efficient p-type doping and hole injection in Al-rich AlGaN devices is highly desirable. A comparison of the proposed multidimensional SLs with the conventional SLs demonstrated a significant enhancement in Mg doping efficiency and excellent p-type conductivity

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Results

Conclusion