MgZnO/ZnO Two-Dimensional Electron Gas Photodetectors Fabricated by Radio Frequency Sputtering

Abstract

MgZnO/ZnO two-dimensional electron gas (2DEG) structures with ZnO annealed at various temperatures (600-900 °C) and photodetectors (PDs) with and without a 2DEG structure were fabricated using a radio frequency magnetron sputtering system. It was found that the carrier concentration and mobility increase with the annealing temperature owing to the improved crystalline in ZnO; however, high-temperature (800 °C or higher) annealing can degrade the crystalline of the ZnO layer. Hall measurements showed that compared with that of bulk ZnO, the sheet carrier concentration of the 2DEG sample increased from 1.3 × 10 to 1.2 × 10 cm, and the mobility was enhanced from 5.1 to 17.5 cm/V s. This is because the channel layer is the total thickness (300 nm) in bulk ZnO, whereas the carriers are confined to a 45 nm region beneath the MgZO layer in the 2DEG sample, confirming the 2DEG behavior at the MgZnO/ZnO interface. The PDs with 2DEG structures demonstrate a higher ultraviolet (UV) response and a UV/visible rejection ratio that is six times larger than that of the PDs without a 2DEG structure. The 2DEG structure also induces a photocurrent gain, which results in a 240% quantum efficiency for the 310 nm incident wavelength. The related mechanism is elucidated with a band diagram.

Barrier thickness dependence of MgxZn1−xO/ZnO quantum well (QW) on the performance of a p-NiO/QW/n-ZnO photodiode

“…Next, Mg x Zn 1Àx O/ZnO/Mg x Zn 1Àx O QW structured layers were consecutively deposited onto the ZnO layer using the same system. 56 The barrier layer thickness of Mg x Zn 1Àx O varies from 10, 25, 40, to 60 nm, while the well layer thickness of ZnO keeps at 4 nm. Finally, the p-NiO with a thickness of 80 nm was deposited using the same RF sputtering system as a hole transport layer.…”

Enhancing the Diode Characteristics of Pulsed Laser–Deposited n‐MgxZn1−xO/p‐Si Heterojunction: Role of Oxygen Ambient Pressure

“…Mg x Zn 1Àx O, a ternary alloy of the wide-bandgap semiconductor ZnO, is a potential material for modern optoelectronic and electronic device applications such as 2D electron gas devices, UV light emitters, photodetectors, and resonant tunneling diodes. [1][2][3][4] Mg x Zn 1Àx O exhibits a large tunable bandgap in the range of %3.3 to 7.8 eV with increase in Mg content from 0 to 100%, variable electrical conductivity by appropriate doping, high transparency (>80%), nontoxicity, and relatively low deposition temperature (100-750 C). [5][6][7][8][9] This large bandgap tunability of Mg x Zn 1Àx O films further extends its applications in UV-A (400-320 nm), UV-B (320-280 nm), and UV-C (280-200 nm) spectral regions.…”

Enhancement of UV Response and Suppression of Visible Response of p-Si/n-ZnO Heterojunction Photodiodes via NiO and MgO Insertion Layers

“…Ultraviolet (UV) photodetectors have been used in commercial and military applications such as flame detection, water purification, ozone layer detection, missile warning systems, etc. Although GaN ( E g = 3.45 eV) and SiC ( E g = 3.26 eV) based UV photodetectors are commercially available, their high growth temperatures (>1000 °C) and large cost make them incompatible for efficient UV photodetectors. , As an alternative, zinc oxide (ZnO) can be deposited using low-cost methods in low temperature environments including radio frequency (RF) sputtering , and solution methods . ZnO has been widely applied in photodetectors, ,− light emitting diodes, , and solar cells , because of its wide band gap (3.3 eV), high transparency in visible wavelengths (>80%), nontoxicity, and large exciton binding energy (60 meV).…”