Evidence of Micron-Scale Ion Damage in (010), (110), and (011) ${\beta}-Ga_2O_3$ Epitaxial Layers

TL;DR

This study demonstrates that ion damage from sputtering and plasma etching causes significant charge depletion in specific orientations of ${eta}-Ga_2O_3$ epitaxial layers, with damage depth up to 11.5 μm, affecting device properties.

Contribution

The paper provides the first experimental evidence of orientation-dependent ion damage depth and its impact on electrical properties in ${eta}-Ga_2O_3$ epitaxial layers.

Findings

Charge depletion up to 11.5 μm deep in certain orientations due to ion damage.

Sputtered heterojunction diodes show increased resistance and reduced donor concentration.

Etched surfaces exhibit significant ion damage effects, especially in (010), (110), and (011) orientations.

Abstract

We report on the experimental observation of up to 11.5 ${\mu}m$ deep charge depletion in (010), (110), and (011) ${\beta}-Ga_2O_3$ epitaxial layers due to ion damage from sputtering and inductively coupled plasma (ICP) etching processes whereas charge depletion in (001) ${\beta}-Ga_2O_3$ epitaxial layers was minimal. The orientation-dependent reduction in CV-measured charge density was first observed in $NiO_x$ reactively sputtered heterojunction p-n diodes (HJDs). When compared to reference low-damage Schottky barrier diodes (SBDs), the sputtered HJDs showed a $9.4{\times}$ increase in the specific on resistance $(R_{on,sp})$ and 85% reduction in net donor concentration $(N_D - N_A)$ at zero bias for sputter-damaged HJDs on (010) epitaxial layers whereas HJDs on (001) remained unchanged. Similarly, sputtered SiO2 caused a reduction of $N_D - N_A$ 11.5 ${\mu}m$ deep into the (010) material. Next, SBDs were fabricated on ${\beta}-Ga_2O_3$ surfaces previously etched via a BCl3 based ICP process and compared to SBDs on un-etched surfaces. The (010) SBDs on etched surfaces exhibited a $7.7{\times}$ increase in $R_{on,sp}$ and a 91% reduction in $N_D - N_A$ at zero bias where the (001) etched diodes exhibited little change. Additionally, (110) and (011) diodes fabricated on ICP damaged surfaces also saw a ~82% reduction in $N_D - N_A$ at zero bias, indicating (110) and (011) are also susceptible to ion damage. Damage in the (010), (110), and (011) diodes is potentially caused by energetic ions that travel into the open channels present along the [010] direction and create compensating point defects which could potentially diffuse further.