Stress and Grain Boundary Properties of GaN Films Prepared by Pulsed Laser Deposition Technique

Abstract

Polycrystalline gallium nitride films were successfully deposited on fused silica substrates by ablating a GaN target using pulsed Nd-YAG laser. Microstructural studies indicated an increase in the average crystallite size from ~8 nm to ~70 nm with the increase in substrate temperature from 300 K to 873 K during deposition. The films deposited here were nearly stoichiometric. XPS studies indicated two strong peaks located at ~1116.6 eV and ~395 eV for Ga2p3/2 and a N1s core-level peak, respectively. The films deposited at substrate temperature above 573 K are predominantly zinc blende in nature. PL spectra of the films deposited at higher temperatures were dominated by a strong peak at ~3.2 eV. FTIR spectra indicated a strong and broad absorption peak centered ~520 cm−1 with two shoulders at ~570 cm−1 and 584 cm−1. Characteristic Raman peak at ~531 cm−1 for the A1(TO) mode is observed for all the films. Grain boundary trap states varied between 3.1×1015 and 7×1015 m−2, while barrier height at the grain boundaries varied between 12.4 meV and 37.14 meV. Stress in the films decreased with the increase in substrate temperature.

Resonant and nonresonant vibrational excitation of ammonia molecules in the growth of gallium nitride using laser-assisted metal organic chemical vapour deposition

“…[23][24][25][26][27] It is generally accepted that grain boundaries impacts negatively on the electrical and optical properties of GaN films. 33,34 Increasing grain sizes leads to reduced grain boundaries and results in a reduced amount of defects and stress. Therefore, the crystalline quality and optical properties of GaN films are improved accordingly.…”

Influence of resonant and non-resonant vibrational excitation of ammonia molecules in gallium nitride synthesis

“…It is generally accepted that grain boundaries exert significant influence on the electrical and optical properties of corresponding GaN films [18][19]. The grain boundary region contains a large amount of defect states, which become charged after trapping free carriers from the neighboring grains [18]. The inherent space charge in grain boundaries region would result in band bending.…”

“…With increases in grain sizes, grain boundaries would decrease, resulting in lesser amount of density of trap states with associated lower stress. Hence, the crystalline quality and optical properties of GaN films are improved [18].…”

Towards electrostatic doping approaches in ultra-thin body semiconductor materials and devices

“…Among several other reported techniques to deposit poly-GaN films such as rf-sputtering [26,28], plasma-assisted molecular beam epitaxy (MBE) [32,34] and pulse laser deposition (PLD) [35], atomic layer deposition (ALD) is an attractive solution [36,37]. ALD features excellent waferlevel uniformity, conformal deposition and, most importantly, critical film thickness control.…”

“…Generally, polycrystalline semiconductor devices do not perform up to par with their crystalline counterparts. For device applications in polycrystalline material several challenges should be taken into consideration [28,35,42], such as obtaining large grain size and reducing the amount of grain boundaries and their role in charge transport, good device stability and reliability, obtaining low defect densities and improving the carrier mobility and lifetime, and good interface control with metals and dielectrics.…”