Daqian Ye

Dual-band MgZnO ultraviolet photodetector integrated with Si

We have constructed a dual-band ultraviolet photodetector by growing high quality MgxZn1−xO layers on Si substrate with molecular beam epitaxy. The device performance was studied by current-voltage, capacitance-voltage, spectra photoresponse, and time-resolved photoresponse characterizations. It demonstrates a high UV/visible light rejection ratio of more than 2 orders of magnitude and a fast response speed of less than 100 ms. The cutoff wavelength can be at solar-blind (280 nm)/visible-blind (301 nm) region by applying 1 V forward/2 V reverse bias. The working principle of the dual-band photodetector was finally investigated by interpretation of the specific carrier transport behavior with the energy band diagram.

Comparative study of n-MgZnO/p-Si ultraviolet-B photodetector performance with different device structures

A comparative study of n-MgZnO/p-Si UV-B photodetector performance was carried out with different device structures. The experimental results demonstrate superior photoresponse characteristics of the p-n heterojunction detector against the Schottky type metal-semiconductor-metal counterpart, including a sharper cutoff wavelength at 300 nm, a larger peak photoresponsivity of 1 A/W, and a faster response speed. The role of built-in field and low interface scattering in p-n heterojunction is explored, and the energy band diagram of n-MgZnO/p-Si is employed to interpret the efficient suppression of visible light photoresponse from Si substrate, revealing the applicability of this heterostructure in fabrication of deep ultraviolet detectors.

Interface engineering of high-Mg-content MgZnO/BeO/Si for p-n heterojunction solar-blind ultraviolet photodetectors

High-quality wurtzite MgZnO film was deposited on Si(111) substrate via a delicate interface engineering using BeO, by which solar-blind ultraviolet photodetectors were fabricated on the n-MgZnO(0001)/p-Si(111) heterojunction. A thin Be layer was deposited on clean Si surface with subsequent in situ oxidation processes, which provides an excellent template for high-Mg-content MgZnO growth. The interface controlling significantly improves the device performance, as the photodetector demonstrates a sharp cutoff wavelength at 280 nm, consistent with the optical band gap of the epilayer. Our experimental results promise potential applications of this technique in integration of solar-blind ultraviolet optoelectronic device with Si microelectronic technologies.

Engineering of optically defect free Cu2O enabling exciton luminescence at room temperature

Cu2O is an interesting semiconductor with extraordinary high exciton binding energy, however exhibiting weak room temperature excitonic luminescence. The issue was addressed in literature emphasizing a detrimental role of native point defects responsible for optical quenching. Resolving the problem, we propose a method to manipulate the Cu and O vacancies contents opening a gateway for optoelectronic applications of Cu2O. Specifically, applying oxygen lean conditions, we observe a remarkable suppression of VCu enabling strong room temperature exciton luminescence, while manipulating with VO reveals no impact on the signal. As a result, the excitonic signature was interpreted in terms of phonon assisted transitions.

Beryllium sites in MBE-grown BeZnO alloy films

We report the possible sites that beryllium atoms can occupy in BeZnO alloy films by a comparative study. The epitaxial BexZn1?xO (x?=?0, 0.06, 0.1, 1) films were prepared by a molecular beam epitaxy technique, and their structural properties were characterized with x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy, while the Be composition, x, was measured with time of flight elastic recoil detection analysis. When x is 6%, substitutional and interstitial Be atoms are revealed to be co-existing in BexZn1?xO films. Furthermore, phase segregation of BeO is observed when x increases to 10% due to the huge difference of the bond length between Be?O and Zn?O. In this case, most of the Be atoms are found to form BeO particles, rather than a BeZnO alloy, so as to reduce the formation energy. The incorporation of Be atoms in the ZnO lattice consequently decreases in Be0.1Zn0.9O, resulting in a smaller bandgap than that of Be0.06Zn0.94O.

A three-terminal ultraviolet photodetector constructed on a barrier-modulated triple-layer architecture

We report a novel three-terminal device fabricated on MgZnO/ZnO/MgZnO triple-layer architecture. Because of the combined barrier modulation effect by both gate and drain biases, the device shows an unconventional I–V characteristics compared to a common field effect transistor. The photoresponse behavior of this unique device was also investigated and applied in constructing a new type ultraviolet (UV) photodetector, which may be potentially used as an active element in a UV imaging array. More significantly, the proper gate bias-control offers a new pathway to overcome the common persistent photoconductivity (PPC) effect problem. Additionally, the MgZnO:F as a channel layer was chosen to optimize the photoresponse properties, and the spectrum indicated a gate bias-dependent wavelength-selectable feature for different response peaks, which suggests the possibility to build a unique dual-band UV photodetector with this new architecture.

Enhancement-mode ZnO/Mg0.5Zn0.5O HFET on Si

We report a bottom-gate and enhancement-mode ZnO/Mg0.5Zn0.5O heterojunction field effect transistor (HFET) on Si. This new heterostructure which is grown by using molecular beam epitaxy (MBE) reduces interface defects and traps. By tailoring Mg composition (x) in the MgxZn1−xO barrier layer up to 50%, the Mg0.5Zn0.5O exhibits insulating properties and the resultant HFET works in an enhancement mode with a field effective mobility of μFE = 21cm2 V−1 s−1, transconductance of gm = 44mSmm−1, on/off ratio of 1 × 105 and off current ~1.33 × 10−8 Amm−1. The device shows good ambient stability.