Effects of fluorine incorporation into β-Ga2O3

Abstract

β-Ga2O3 rectifiers fabricated on lightly doped epitaxial layers on bulk substrates were exposed to CF4 plasmas. This produced a significant decrease in Schottky barrier height relative to unexposed control diodes (0.68 eV compared to 1.22 eV) and degradation in ideality factor (2.95 versus 1.01 for the control diodes). High levels of F (>1022 cm−3) were detected in the near-surface region by Secondary Ion Mass Spectrometry. The diffusion of fluorine into the Ga2O3 was thermally activated with an activation energy of 1.24 eV. Subsequent annealing in the range 350–400 °C brought recovery of the diode characteristics and an increase in barrier height to a value larger than in the unexposed control diodes (1.36 eV). Approximately 70% of the initial F was removed from the Ga2O3 by 400 °C, with the surface outgas rate also being thermally activated with an activation energy of 1.23 eV. Very good fits to the experimental data were obtained by integrating physics of the outdiffusion mechanisms into the Florida Object Oriented Process Simulator code and assuming that the outgas rate from the surface was mediated through fluorine molecule formation. The fluorine molecule forward reaction rate had an activation energy of 1.24 eV, while the reversal rate of this reaction had an activation energy of 0.34 eV. The net carrier density in the drift region of the rectifiers decreased after CF4 exposure and annealing at 400 °C. The data are consistent with a model in which near-surface plasma-induced damage creates degraded Schottky barrier characteristics, but as the samples are annealed, this damage is removed, leaving the compensation effect of Si donors by F− ions. The barrier lowering and then enhancement are due to the interplay between surface defects and the chemical effects of the fluorine.

Recent progress on the effects of impurities and defects on the properties of Ga2O3

“…). 308,309 The experimental results about the surface of Ga 2 O 3 absorbed by the different impurities showed that different surface treatments had different effects on the electronic properties ( e.g. , Schottky barrier height, etc .)…”

“…For example, Yang et al investigated the bulk Ga 2 O 3 materials after surface treatment such as plasma treatment (CF 4 and O 2 ), gaseous treatment (ultraviolet/O 3 ), and liquid treatment (HCl, H 2 O 2 , etc.). 308,309 The experimental results about the surface of Ga 2 O 3 absorbed by the different impurities showed that different surface treatments had different effects on the electronic properties (e.g., Schottky barrier height, etc.) of bulk Ga 2 O 3 .…”

Growth and characterization of metalorganic vapor-phase epitaxy-grown β-(Al x Ga1−x )2O3/β-Ga2O3 heterostructure channels

“…24) TLM measurements on the regrown n + layer without any channel layer, showed a ρ c ∼ 10 −6 Ω cm 2 indicating low resistance n + Ga 2 O 3 /Ti contact. The high R c is attributed to etch damage and charge depletion due to fluorine ions 31) resulting from the SF 6 /Ar dry etch step used before the contact regrowth step. Switching to BCl 3 /Ar chemistry-based dry etch step could lead to lower contact resistivity.…”

Effects of Downstream Plasma Exposure on β-Ga2O3 Rectifiers

“…23 However, it is not widely appreciated that the surface of β-Ga 2 O 3 can be strongly affected by exposure to gaseous or plasma environments and the influence of changing conductivity and roles of surface states in oxidizing or reducing environments are not well-established. [24][25][26][27][28][29][30][31][32][33][34][35][36][37] This is despite the fact that Ga 2 O 3 rectifiers are known to be sensitive detectors of hydrogen. 25,26 The (−201) Ga 2 O 3 surface has been reported to be particularly sensitive to plasma-induced damage, leading to device performance degradation.…”

“…This work complements previous studies where the Ga 2 O 3 was exposed to these plasmas in immersive mode, where combined chemical and physical bombardment effects are present. 24,28,29…”