Twist's Review #11 - Amorphous Layer in Ga2O3 Schottky Barrier Diode

Paper: Effect of Amorphous Layer at the Heterogeneous Interface on the Device Performance of β-Ga2O3/Si Schottky Barrier Diodes

I have covered some power devices previously, but this will be my first time covering a β-Ga2O3 based power device, specifically a Schottky barrier diode (SBD). Now β-Ga2O3 is a material that is attracting attention for power devices, and has been for the past few years due to its ultra wide band gap and extremely high breakdown field strength of 8 MV/cm. Another advantage of β-Ga2O3 is that it is scalable, in the sense that large-size β-Ga2O3 single crystals can be fabricated using a method that is also used for Si which is the melt-grown method. Due to this, its figure of merit surpasses that of SiC and GaN albeit with its own unique set of challenges (e.g. thermal conductivity).

This paper was written by group in China, spanning different parts of the country (Beijing, Shanghai and Xi’an). The paper initially notes that an amorphous layer of Ga2O3 exists between β-Ga2O3 and the wafer, in this case Silicon (as it can accomodate for β-Ga2O3’s low thermal conductivity). This layer appears at the interfce as a result of using the ion-cutting technique method to grow the β-Ga2O3 on the Si, which is limited in regards to surface activation bonding, induced by Ar bombardment during the bonding process. Although the amorphous layer can be eliminated by high temperature annealing, interdiffusion of elements is very concerning at these temperatures.

Alas, the authors decide to investigate the effect of this amorphous layer to a SBD. In the devices they fabricated, an amorphous layer of about 4nm was observed using TEM. Additionally, a 900 C annealing was done for 30 minutes and by using energy dispersive spectroscopy it was found that a thicker amorphous layer was observed due to interdiffusion of Ga, O and Si.

Ga2O3 bulk SBDs were also fabricated along with the Ga2O3/Si SBDs and its J-V characteristics were measured (simulations were also done for both SBDs for further investigations). The Ga2O3 bulk SBD hit compliance after about 3V of applied voltage, while the Ga2O3/Si SBD had over 5x less current flowing even after 10V of applied voltage. After further study, it was found that most of the resistance (Ron) that results in the inferior current is the amorphous layer.

Using TCAD and calibrating to the measured results, simulations were done to see the impact of the thickness of the amorphous layer and mole fraction (fraction of β-Ga2O3 over total between β-Ga2O3 and SiO2). An increase in mole fraction seems to increase current density for the SBD (due to the higher fraction of Ga diffusion lowering the barrier height due to the amorphous layer), and a thinner amorphous layer also results in a better SBD (higher current density, better Ron stability).

[1] Z. Qu et al., “Effect of Amorphous Layer at the Heterogeneous Interface on the Device Performance of β-Ga2O3/Si Schottky Barrier Diodes,” in IEEE Journal of the Electron Devices Society, vol. 11, pp. 135-140, 2023, doi: 10.1109/JEDS.2023.3242968.
keywords: {Silicon;Surface treatment;Semiconductor process modeling;Performance evaluation;Fabrication;Surface topography;Schottky barriers;Schottky barrier diode;hetero-interface;TCAD simulation},

I always wanted to read on Ga2O3, and while I have done that before I wanted to read up on a recent paper to follow its recent findings. Ga2O3 is another material that is on that “list” of high potential electronic materials along with AlN, and Diamond for power devices. Anyway, IEDM 2023 proceedings just got released and while I am excited to read them unfortunately they are not open access. So I’ll look through them for now and bother one of my friends who does have access to pass the document over to me :smile: