Role of self-trapped holes in the photoconductive gain of β-gallium oxide Schottky diodes

Abstract

Solar-blind photodetection and photoconductive gain >50 corresponding to a responsivity >8 A/W were observed for β-Ga2O3 Schottky photodiodes. The origin of photoconductive gain was investigated. Current-voltage characteristics of the diodes did not indicate avalanche breakdown, which excludes carrier multiplication by impact ionization as the source for gain. However, photocapacitance measurements indicated a mechanism for hole localization for above-band gap illumination, suggesting self-trapped hole formation. Comparison of photoconductivity and photocapacitance spectra indicated that self-trapped hole formation coincides with the strong photoconductive gain. It is concluded that self-trapped hole formation near the Schottky diode lowers the effective Schottky barrier in reverse bias, producing photoconductive gain. Ascribing photoconductive gain to an inherent property like self-trapping of holes can explain the operation of a variety of β-Ga2O3 photodetectors.

High responsivity in molecular beam epitaxy grown β-Ga2O3 metal semiconductor metal solar blind deep-UV photodetector

“…The measured photo current (I ph m ) consists of two components: an intrinsic bias-independent photo current I ph 0 , and the component arising due (1) Using equation (1), the barrier lowering (ΔΦ B ) due to trapping of holes is estimated to be ~ 0.27 eV as shown in the inset of the Fig (4(a)). This is in good agreement with the value of ΔΦ B ~ 0.3 eV reported by Armstrong et al 25 .…”

“…This is a clear indication of the gain in the devices. Hole trapping has been suggested as one of the several possible 25 gain mechanisms in MSM photodetectors. We predict that the high gain resulting in high responsivity in the devices is due to the localization of the self-trapped holes at the interface of the metal and the semiconductor 25 .…”

Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

“…[21][22][23] DLOS results have only been reported for UID EFG material for (010) and (-201) orientations. 8,11 Given TABLE I. Summary of DLOS-detected defect energy levels and associated Frank-Condon energies associated with the SSPC onset energies listed and shown in Fig.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Interest is also rising for possible applications as a deep ultraviolet solar blind detector due to its outstanding transparency out to $260 nm. 10,11 However, perhaps the primary driver for the interest is that b-Ga 2 O 3 , with its $4.5-4.9 eV bandgap, 2 is available as a bulk crystal, and therefore, native substrates are available for lattice-matched epitaxial growth of device structures, unlike contemporary wide and ultrawide bandgap semiconductors.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Interest is also rising for possible applications as a deep ultraviolet solar blind detector due to its outstanding transparency out to $260 nm. 10,11 However, perhaps the primary driver for the interest is that b-Ga 2 O 3 , with its $4.5-4.9 eV bandgap, 2 is available as a bulk crystal, and therefore, native substrates are available for lattice-matched epitaxial growth of device structures, unlike contemporary wide and ultrawide bandgap semiconductors. In spite of the early stage of development, promising device demonstrations have already been reported, including metal-semiconductor field effect transistors (MESFETs), 1 metal-oxide field effect transistors (MOSFETs), [2][3][4][5] Schottky diodes, [6][7][8][9] FinFETs, 12 delta-doped FETs, 13 and (Al 1-x Ga x ) 2 O 3 /Ga 2 O 3 modulation-doped field effect transistors (MODFETs) grown by plasma-assisted molecular beam epitaxy (PAMBE).…”