Formation and control of the E2∗ center in implanted β-Ga 2 O 3 by reverse-bias and zero-bias annealing

Abstract

Deep-level transient spectroscopy measurements are conducted on β-Ga 2 O 3 thin-films implanted with helium and hydrogen (H) to study the formation of the defect level E 2 ∗ ( E A = 0.71 eV) during heat treatments under an applied reverse-bias voltage (reverse-bias annealing). The formation of E 2 ∗ during reverse-bias annealing is a thermally-activated process exhibiting an activation energy of around 1.0 eV to 1.3 eV, and applying larger reverse-bias voltages during the heat treatment results in a larger concentration of E 2 ∗ . In contrast, heat treatments without an applied reverse-bias voltage (zero-bias annealing) can be used to decrease the E 2 ∗ concentration. The removal of E 2 ∗ is more pronounced if zero-bias anneals are performed in the presence of H. A scenario for the formation of E 2 ∗ is proposed, where the main effect of reverse-bias annealing is an effective change in the Fermi-level position within the space-charge region, and where E 2 ∗ is related to a defect complex involving intrinsic defects that exhibits several different configurations whose relative formation energies depend on the Fermi-level position. One of these configurations gives rise to E 2 ∗ , and is more likely to form if the Fermi-level position is further away from the conduction band edge. The defect complex related to E 2 ∗ can become hydrogenated, and the corresponding hydrogenated complex is likely to form when the Fermi level is close to the conduction band edge. Di-vacancy defects formed by oxygen and gallium vacancies (V O −V G a ) fulfill several of these requirements, and are proposed as potential candidates for E 2 ∗ .

Interplay of vacancies, hydrogen, and electrical compensation in irradiated and annealed n-type β-Ga2O3

“…Furthermore, the calculated O-D stretch modes of D-containing unshifted V Ga1 and V Ga2 defects should be polarized along the [010] lattice vector 26,27,35 showed that H trapping and relaxation processes in β -Ga 2 O 3 make it highly unlikely that any of the hydrogenated unshifted V Ga will occur. 35 Interestingly, recent experimental 16 and theoretical work 19 have suggested that V Ga -V O divacancy complexes could give rise to the so-called E2* level observed using DLTS in β -Ga 2 O 3 single crystals after H-and He-irradiation. Importantly, the positron annihilation signature of a cation vacancy is expected to remain relatively unchanged compared to its complex with a small anion vacancy 25,36 .…”

“…Recent studies utilizing deep-level transient spectroscopy (DLTS) have shown that irradiation also gives rise to two charge state transition levels labeled E2* and E4. 4,[14][15][16] Annealing the samples at 600 K removes the E4 level but also increases the concentration of E2*. 4 In fact, E2* has been shown limit a) Electronic mail: antti.j.karjalainen@iki.fi the performance β -Ga 2 O 3 -based metal-semiconductor field effect (MESFET) transistors 17,18 and suggested to originate from V Ga -V O divacancy defect complexes.…”

“…4 In fact, E2* has been shown limit a) Electronic mail: antti.j.karjalainen@iki.fi the performance β -Ga 2 O 3 -based metal-semiconductor field effect (MESFET) transistors 17,18 and suggested to originate from V Ga -V O divacancy defect complexes. 16,19 One of the difficulties in studying intrinsic point defects in β -Ga 2 O 3 is the large number of V Ga configurations. Theory finds that monovacancies of both of the inequivalent Ga sites (V Ga1 and V Ga2 ), are metastable, and exhibit rather low energy barriers (<0.5 eV) to relax into "split-interstitial" (or shifted) configurations (V i Ga ) in n-type material.…”

Multistability of isolated and hydrogenated Ga–O divacancies in β−Ga2O3

“…Recently, the authors of this article reported on the formation of E * 2 in β-Ga 2 O 3 subjected to H and/or He implantation, as measured by DLTS on Schottky barrier diodes. It was found that the introduction of E * 2 is promoted when performing a subsequent annealing * ymirkf@fys.uio.no at 650 K under an applied reverse-bias voltage (reverse-bias annealing) [8]. Conversely, heat treatments without an applied reverse-bias voltage (zero-bias annealing) lead to a decrease in the E * 2 concentration, which is more pronounced in the presence of H. Moreover, simulations of DLTS spectra suggest that E * 2 consists of several overlapping signatures [8].…”

“…It was found that the introduction of E * 2 is promoted when performing a subsequent annealing * ymirkf@fys.uio.no at 650 K under an applied reverse-bias voltage (reverse-bias annealing) [8]. Conversely, heat treatments without an applied reverse-bias voltage (zero-bias annealing) lead to a decrease in the E * 2 concentration, which is more pronounced in the presence of H. Moreover, simulations of DLTS spectra suggest that E * 2 consists of several overlapping signatures [8]. Based on these experimental results, it was proposed that the most likely origin of E * 2 is a defect complex involving intrinsic defects, which can interact with H donors, and exist in several different configurations, where the configurations giving rise to E * 2 are more likely to form when the Fermi level is shifted away from the conduction band minimum (CBM), i.e., in the space-charge region of Schottky barrier diodes.…”