Two-dimensional electron gas in Zn-polar ZnMgO/ZnO heterostructure grown by metal-organic vapor phase epitaxy

Yarar

et al. 2015

Journal of Elec Materi

The electron-transport properties of a Zn 1Àx Mg x O/ZnO hetero structure were studied by use of an ensemble Monte Carlo technique. There was no intentional doping in the profile and the entire charge is because of polarization of charges at the interface. Interface roughness, and the intensity of acoustic and optic phonon scattering were used in the ensemble Monte Carlo method to find the transport properties of the two-dimensional electron gas (2DEG). The lowfield mobility characteristics of the structure were determined as a function of temperature, the thickness of the ZnMgO layer, and the interface roughness. The interface roughness was found to have a very large effect on the drift mobility of carriers, especially at low temperatures. It was observed that as the thickness of the ZnMgO increases the concentration of electrons increases whereas the mobility of the electrons decreases. The low-field mobility values obtained from ensemble Monte Carlo simulations were in agreement with published experimental data.

Section: Introductionmentioning

confidence: 93%

Electron-Transport Properties of a ZnMgO/ZnO Hetero Structure and the Effect of Interface Roughness and ZnMgO Thickness

Yarar

et al. 2015

Journal of Elec Materi

Physica Status Solidi (a)

“…This can be achieved by intentional variation of the fluxes/partial pressures during growth in molecular beam epitaxy (MBE) or the variation of precursor fluxes in metal‐organic vapor phase epitaxy (MOVPE). For MBE and MOVPE (unintentional) vertical composition gradients have been reported for (Mg,Zn)O due to the “composition‐pulling effect.” Also for pulsed laser deposition, a scheme has been developed to fabricate vertically composition graded layers using radially segmented targets …”

Section: New Concept For a Monolithic Wavemetermentioning

confidence: 99%

Monolithic Forward‐Looking Photodetector for Use as Ultra‐Compact Wavemeter with Wide Spectral Range

Grundmann

2018

A monolithic, forward‐looking photodetector that can be used as a wavemeter is proposed. The device consists of two vertically stacked photosensitive layers that can be read out separately. The top photodetector contains a vertical gradient of semiconductor alloy composition, leading to a designed, broad, ideally linearly increasing absorption edge. The bottom photodetector is sensitive to all wavelengths falling into the device. The ratio of the two photosignals is related to the wavelength of monochromatic incoming radiation. The spectral range of the device is determined by the used alloy compositions. The device response for the (Mg,Zn)O material system with sensitivity in the ultraviolet spectral range is simulated.

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

“…However, recent calculations show that oxygen vacancies are actually a deep-level donor ͑0.7 eV below the conduction band minimum͒, 19,20 leading to an ultralow activation rate of free electrons at room temperature. This could be ascribed to the poor crystal quality and the relatively small domains.…”

Section: B Electrical Propertiesmentioning

confidence: 99%

Influence of thermally diffused aluminum atoms from sapphire substrate on the properties of ZnO epilayers grown by metal-organic chemical vapor deposition

Tang¹,

Gu²,

Li³

et al. 2011

Residual and intentional n-type doping of ZnO thin films grown by metal-organic vapor phase epitaxy on sapphire and ZnO substrates Electrical and optical studies of metal organic chemical vapor deposition grown N-doped ZnO films Correlation between exciton-phonon interaction and electrical conductivity for unintentionally-doped ZnO epilayers grown by metal-organic chemical vapor deposition J. Appl. Phys.In this study, the authors investigate the evolution of the structural and electrical properties of ZnO epilayers grown by the metal-organic chemical vapor deposition method on c-sapphire substrates. The inserting of a low-temperature ZnO buffer layer not only significantly improves the structural quality of the high-temperature ͑HT͒-grown ZnO epilayer on a sapphire substrate but also results in high background electron concentration in it from the Hall-effect measurement. After subtracting the conductive contribution from a thin degenerated layer mostly formed between the buffer layer and the substrate based on the two-layer model, the deduced electron-carrier concentration is still in the order of 10 18 cm −3 , which is much larger than the 10 16 cm −3 obtained from capacitance-voltage measurement near the top surface. This indicates that a much thicker layer with high carrier concentration should be formed in the HT-grown ZnO epilayer, which is significantly different from that observed in GaN epitaxy, where only a thin degenerated interfacial layer is suggested to form in the GaN buffer layer. Al atoms' distribution acquired from secondary-ion mass spectrometry shows a strong dependence on the temperature of the ZnO growth process, indicating that a thermally enhanced diffusion mechanism should be responsible for the observation of the enhanced Al atom concentration in the HT-grown ZnO epilayer. As substituted Al atoms on the Zn site act as donors in ZnO, the one-to-one correspondence between Al content and the carrier concentration, as well as the analysis of temperature-dependent Hall-effect measurement, indicates that diffusion-induced gradient-distributed Al Zn shallow donors should be the main origin of the high background-carrier concentration in the HT-grown ZnO epilayers.