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Novel devices based on orthorhombic κ - Ga 2 O 3 could enable solar blind infrared detection or high-electron mobility transistors with large two-dimensional electron gas densities. Here, we report on the current transport parallel to the growth direction of κ - Ga 2 O 3 layers grown by pulsed-laser deposition on highly conductive Al-doped ZnO back contact layers. Besides ohmic Ti/Al/Au contact layer stacks, vertical Pt / PtO x / κ - Ga 2 O 3 and Pd / PdO x / κ - Ga 2 O 3 Schottky barrier diodes and NiO / κ - Ga 2 O 3 and ZnCo 2 O 4 / κ - Ga 2 O 3 p n -heterodiodes are investigated by current–voltage measurements. While a lateral current transport is severely suppressed to less than 10 − 9 A cm − 2 due to rotational domains, we record a significant current flow through the ohmic contacts in the vertical direction of > --> 0.1 A cm − 2 . The Schottky barrier diodes and the p n -heterojunctions exhibit rectification ratios of up to seven orders of magnitude. Room temperature current–voltage characteristics of diode ensembles as well as temperature-dependent measurements for selected Pt-based diodes reveal a mean barrier height of ϕ B m ≈ 2.1 eV and ideality factors down to η ≈ 1.3. [ABSTRACT FROM AUTHOR]

Schottky barrier diodes on α − Ga 2 O 3 :Sn heteroepitaxial thin films grown by pulsed laser deposition on m-plane sapphire substrates are reported. Sets of co-planar diodes were fabricated with different metals and different deposition methods. The current rectification and effective Schottky barrier height of oxidized contacts realized by reactive sputtering significantly exceed the values of non-oxidized contacts realized by thermal evaporation or sputtering in an inert argon atmosphere. The best values obtained are rectification of about eight orders of magnitude (± 2 V) and 1.3 eV effective barrier height. The current-voltage characteristics of selected non-oxidized and oxidized platinum diodes have been studied as a function of measurement temperature. The temperature dependence of the effective barrier height and the ideality factor of the diodes were fitted taking into account the lateral potential fluctuations of the barrier potential. The determined mean barrier heights and standard deviations are in the range of 1.76–2.53 and 0.2–0.33 eV, respectively, and are classified with respect to the literature and fulfill a well-established empirical correlation (Lajn's rule) for a variety of Schottky barrier diodes on different semiconducting materials. [ABSTRACT FROM AUTHOR]

The article studies the current-voltage mechanism of low-ideality factor ZnO Schottky diodes over temperature range of 40-423 K. Findings revealed that TE was a major current transport mechanism at RT and above.

We determined the dielectric function of the alloy system (AlxGa1-x)2O3 by spectroscopic ellipsometry in the wide spectral range from 0.5 eV to 8.5 eV and for Al contents ranging from x=0.11 to x=0.55. For the composition range x<0.4, we observe single phase material in the β-modification and for larger Al content also the occurrence of γ-(Al,Ga)2O3. We derived spectra of the refractive index and the absorption coefficient as well as energy parameters of electronic bandband transitions by model analysis of the dielectric function. The dependence of the dielectric functions lineshape and the energy parameters on x is highly continuous, reflecting theoretical expectations. The data presented here provide a basis for a deeper understanding of the electronic properties of this material system and may be useful for device engineering. [ABSTRACT FROM AUTHOR]

We determined the dielectric function of the alloy system (InxGa1–x)2O3 by spectroscopic ellipsometry in the wide spectral range from 0.5 eV to 8.5 eV and for In contents ranging from x=0.02 to x=0.61. The predicted optical transitions for binary, monoclinic β-Ga2O3, and cubic bcc-In2O3 are well reflected by the change of the dielectric functions' lineshape as a function of the In content. In an intermediate composition range with phase-separated material (x≈0.3...0.4), the lineshape differs considerably, which we assign to the presence of the high-pressure rhombohedral InGaO3-II phase, which we also observe in Raman experiments in this range. By model analysis of the dielectric function, we derived spectra of the refractive index and the absorption coefficient and energy parameters of electronic band-band transitions. We discuss the sub-band gap absorption tail in relation to the influence of the In 4d orbitals on the valence bands. The data presented here provide a basis for a deeper understanding of the electronic properties of this technologically important material system and may be useful for device engineering. [ABSTRACT FROM AUTHOR]

Transparent metal-insulator-semiconductor field-effect transistors (TMISFETs) are commonly designated as one keystone of transparent circuitry. TMISFETs were demonstrated using carbon nanotubes, organics, or oxides. The optimization of their gate-insulator as well as the field-effect mobility and switching voltages is of major interest in this research field. We present an alternative approach based on metal-semiconductor field-effect transistors (MESFETs) circumventing these problems of TMISFET technology. We use ultrathin transparent rectifying contacts (TRCs) consisting of non-insulating AgxO or PtxO layers and a highly conducting capping layer realized by room-temperature sputtering. The process is compatible with other low-temperature, low-cost manufacturing steps. We demonstrate the potential of such TRCs for ZnO-based MESFETs having a transparency of 70% in the visible, on/off-ratios higher than 106 within a gate-voltage sweep of only 2.7 V and mobilities up to 12 cm2/V s. Inverters fabricated from these transistors exhibit maximum gain of 196 and uncertainty level of 0.36 V, outperforming inverters based on TMISFETs. [ABSTRACT FROM AUTHOR]