Electrical properties of ZnO/GaN heterostructures and photoresponsivity of ZnO layers

Abstract

We report on the electrical properties of ZnO/GaN heterostructures and the photoresponsivity of ZnO Schottky barrier diodes for the applications of heterojunction transistors and ultraviolet photodetectors, respectivly. ZnO/GaN heterostructures exhibit a large plateau region of 6.5 V in 10 kHz capacitance-voltage curves. Moreover, it is found that a high electron density of ~ 10 18 cm -3 is accumulated at the heterointerface in depth profile. ZnO Schottky barrier diodes show a rapid increase of photocurrent of ~ 10 2 A at the long-wavelength cutoff of 390 nm with maitaining stable diode characteristics. And, it is observed that ZnO Schottky barrier diodes respond to photosignal within 1 ~ 2 msec with a time constant of 0.35 msec. ZnO/GaN heterostructures are very attractive as heterojunction devices, because a large bandgap discontinuity at heterointerface is expected. Johnson et al. have reported that the valence band of GaN is estimated to be located at 0.6 eV above the valence band of ZnO based on the electron affinity rule [2]. Hong et al. have by using X-ray photoelectron spectroscopy observed that the ZnO/GaN heterointerface is made up of the type II band alignment with the valence-band offset of 0.8 eV [3]. Moreover, ZnO/GaN heterostructures also have attractive merits in the aspect of crystal growth. GaN is good choice for a template for ZnO growth, because ZnO is a closely lattice-matched material to GaN with a lattice mismatch of 1.8 % [4], which is ten times smaller than Al 2 O 3 that is normally used as a substrate for ZnO. In the case that GaN with Ga polarity is used as a template, the polarity of ZnO can also be easily controlled by changing preexposure conditions [5].ZnO is also very attractive as UV photodetecting devices, because its bandgap spans the spectral region ranging from 2.5 eV (496 nm) to 10.6 eV (124 nm) by alloying Oxide materials such as CdO, MgO, and BeO. Moreover, ZnO is more strong for radiation damage at the range of very short wavelength (< 200 nm) than Si and GaN, due to large radiation hardness [1].

Semiconductor ultraviolet photodetectors based on ZnO and MgxZn1−xO

“…What is more, p-type GaN is readily available. Hence, it is the most promising for ZnO heterojunction preparation with low interface defects [165]. A band-pass n-ZnO/p-GaN photodiode has been invented with MBE growth techniques [166].…”

Hybrid density functional study of band alignment in ZnO–GaN and ZnO–(Ga1−xZnx)(N1−xOx)–GaN heterostructures

“…Considerable efforts have been made to determine this parameter both experimentally [10][11][12] and theoretically. [13][14][15] However, these works gave quite different values.…”

Structural and optical properties of ZnO films obtained on mesoporous Si substrates by the method of HF magnetron sputtering

“…To obtain ZnO epitaxial films the substrates of gallium nitride [6] and silicon carbide [7] can be used.…”