Atomic layer deposited α-Ga₂O₃ solar-blind photodetectors

Abstract

Low temperature atomic layer deposition was used to deposit α-Ga2O3 films, which were subsequently annealed at various temperatures and atmospheres. The α-Ga2O3 phase is stable up to 400 o C, which is also the temperature that yields the most intense and sharpest reflection by X-ray diffraction. Upon annealing at 450 o C and above, the material gradually turns into the more thermodynamically stable ε or β phase. The suitability of the materials for solar-blind photodetector applications has been demonstrated with the best responsivity achieved being 1.2 A/W under 240 nm illumination and 10 V bias, for the sample annealed at 400 o C in argon. It is worth noting however that the device performance strongly depends on the annealing conditions, with the device annealed in forming gas behaving poorly. Given that the tested devices have similar microstructure, the discrepancies in device performance are attributed to hydrogen impurities.

Ti Alloyed α-Ga2O3: Route towards Wide Band Gap Engineering

“…(Annealing the samples at ca. 400 o C has been shown to release that residual strain [7].) Interference fringes can be distinguished on the base of the diffraction peak, with a spacing that is representative of the film thicknesshere 28 nm, in reasonable agreement with the thickness estimated by ellipsometry (Table I).…”

“…As the concentration of Ti increases, the intensity of the peaks decreases rapidly, vanishing for sample 10%Ti, suggesting that the samples are undergoing a phase change, most likely to an amorphous phase. There is a second peak in the scan for the 5%Ti sample, which appears at a lower angle (~38 o ), possibly indicating the emergence of one or more other phase, such as β-Ga2O3 and ε-Ga2O3 [7,46]. However, the peak is less intense than the already weak α-Ga2O3 0006 reflection, suggesting that at this concentration of Ti, the alloy is already mostly amorphous.…”

“…Alpha phase gallium oxide (α-Ga2O3) is an ultra-wide band gap semiconductor, with most measurements of its band gap lying between 5.1 eV and 5.3 eV [1][2][3][4][5]. It is of particular interest for application in solar-blind ultraviolet (UV) photodetectors [2,4,6,7]. Uses for photodetectors that can absorb efficiently in this regime, of wavelengths <285 nm, include water and air purification systems [8], flame detection, UV astronomy, missile defence systems and engine monitoring [4,9].…”

Study of Ti contacts to corundum α-Ga2O3

“…All the XRD diffractograms (figures 1 and S1) exhibited a clear 0006 reflection from the α-Al 2 O 3 substrate at 2θ = 41.68 • , and a 0006 reflection from the α-Ga 2 O 3 film at 2θ = 40.16 • -close to its relaxed value at 40.25 • [19]. Upon annealing, the α-Ga 2 O 3 reflection was observed to shift towards its relaxed value, indicating that strain relaxation occurs upon annealing, as was reported by Moloney et al [20]. We explain this strain relaxation to the motion of misfit dislocations which were already present at the substrate/film interface in the samples before annealing [15].…”

Efficient organic solar cells with low-temperature in situ prepared Ga2O3 or In2O3 electron collection layers

“…Ga 2 O 3 is a wide-bandgap semiconductor with ultrahigh transparency in the ultraviolet and visible wavelength (UV-vis) regions [22]. It is usually fabricated by atomic layer deposition [23], hydrothermal method [24], or chemical vapor deposition [25], and the fabrication or annealing temperature is usually higher than 400°C, which is unsuitable for OSCs. Furthermore, no literature regarded the application of Ga 2 O 3 in OSCs.…”