Thermal Stability of Schottky Contacts and Rearrangement of Defects in β‐Ga₂O₃ Crystals

Abstract

The thermal stability of different Schottky contacts (Au, Pt, and Ni) on (100) β‐Ga2O3 single crystals grown by the Czochralski method is investigated. Besides the examination of the Schottky barrier parameters, contact‐dependent defect levels are investigated by deep‐level transient spectroscopy (DLTS) in a 100–650 K (ramp‐up) and 650–100 K (ramp‐down) temperature cycle. Several defect levels are detected below the conduction band minimum at 0.41, 0.60, 0.77, 0.96, and 1.17 eV. In the temperature ramp‐down DLTS, the 1.17 eV level disappears, and the 0.60 eV level appears for all Schottky contacts. DFT calculations suggest that rearrangement and dissociation of a single hydrogen from a doubly‐hydrogenated Ga─O divacancy complex occurs during the temperature sweep under bias. The trap level at 0.96 eV only appears after the thermal load for the Ni contact, in contrast to Au and Pt, where it is present without a thermal budget. Temperature‐dependent leakage current (at −4 V) measurements indicate oxidation of Ni, and further thermodynamic analysis suggests alloying of Au‐Ga atoms at the Au/β‐Ga2O3 interface. These studies provide insight into the behavior induced by these common Schottky contacts and the alteration associated with temperature cycling.

Perspective on electrically active defects in β-Ga2O3 from deep-level transient spectroscopy and first-principles calculations

“…Here, it should be pointed out that starting from the temperature range where E 3 is observed and up to 650 K, irradiation produces several overlapping signatures that display larger uncertainties in the extracted activation energies and can disappear after multiple DLTS cycles up to 650 K. 38 The second observation that has been challenging to explain within the Ti Ga2 model comes from a recent study on the thermal stability of different Schottky contacts (Au, Pt, and Ni) on CZ-grown β-Ga 2 O 3 . 53 Here, the E 3 center was present already in the first measurement from 100 to 650 K (ramp-up) in freshly processed samples with Au and Pt contacts but appeared in the sample with Ni contacts only after being subjected to the thermal load, i.e., in the measurement from 650 to 100 K (ramp-down). 53 Further studies are required to explain these observations.…”

“…53 Here, the E 3 center was present already in the first measurement from 100 to 650 K (ramp-up) in freshly processed samples with Au and Pt contacts but appeared in the sample with Ni contacts only after being subjected to the thermal load, i.e., in the measurement from 650 to 100 K (ramp-down). 53 Further studies are required to explain these observations.…”

“…Such effects have been invoked to explain certain experimental observations on DLTS signatures in β-Ga 2 O 3 . 9,19,38,52,53 There are also practical implications of the metastability; external stimuli such as temperature or electrical field can transform the defect from a passive configuration into a useful or harmful 54,55 one for device operation.…”

“…A specific defect model for E 4 was recently proposed by Palvan et al 53 in their study on the thermal stability of different Schottky contacts on CZ-grown β-Ga 2 O 3 . The E 4 center was present in the temperature ramp-up DLTS spectrum for all freshly processed diodes but disappeared after the thermal load and did not recover over time.…”

A Review of β-Ga2O3 Power Diodes

“…This attribute endows β-Ga2O3 with significant potential in the domain of two-dimensional materials and devices [63][64][65][66]. The growth techniques for β-Ga 2 O 3 single-crystal substrates predominantly encompass the Czochralski method (CZ) [15,18,67], optical floating zone method (OFZ) [68][69][70], vertical Bridgman method (VB) [71][72][73], and edge-defined film-fed growth method (EFG) [17,[74][75][76][77], among which the EFG is the most mature, offering the potential for mass production and cost efficiency. In 2018, Japan's Novel Crystal Technology Inc. (Saitama, Japan) pioneered the fabrication of 6-inch β-Ga 2 O 3 single-crystal substrates using the EFG method.…”