We have synthesized CdxZn1−xO alloys across the full composition range. The structural mismatch of the two endpoint compounds splits the alloy into two regions of distinct optical and electrical behavior. The wurtzite phase alloys at compositions 0 < x < 0.69 exhibit a decrease in the absorption edge across the visible range and an increase in the conductivity with increasing Cd content. A phase transition to the rocksalt structure is observed above x = 0.69 along with a step increase in the electron mobility and the absorption edge. The intrinsic bandgap of these alloys was determined taking into account the carrier filling and renormalization effects.

We have measured the band edge energies of Cd x Zn 1Àx O thin films as a function of composition by three independent techniques: we determine the Fermi level stabilization energy by pinning the Fermi level with ion irradiation, measure the binding energy of valence band states and core levels by X-ray photoelectron spectroscopy, and probe shifts in the conduction band and valence band density of states using soft X-ray absorption and emission spectroscopy, respectively. The three techniques find consensus in explaining the origin of compositional trends in the optical-bandgap narrowing upon Cd incorporation in wurtzite ZnO and widening upon Zn incorporation in rocksalt CdO. The conduction band minimum is found to be stationary for both wurtzite and rocksalt alloys, and a significant upward rise of the valence band maximum accounts for the majority of these observed bandgap changes. Given these band alignments, alloy disorder scattering is found to play a negligible role in decreasing the electron mobility for all alloys. These band alignment details, combined with the unique optical and electrical properties of the two phase regimes, make CdZnO alloys attractive candidates for photoelectrochemical water splitting applications.

We have synthesized alloys of NiO and CdO that exhibit an extreme type III band offset and have studied the structural, electrical, and optical properties of Ni x Cd 1Àx O over the entire composition range. The alloys are rocksalt structured and exhibit a monotonic shift of the (220) diffraction peak to higher 2h angles with increasing Ni concentration. The electron mobility and electron concentration decrease with increasing x, and samples become insulating for Ni content x > 0.44. This decrease in n-type conductivity is consistent with the movement of the conduction band minimum from below to above the Fermi stabilization energy with increasing Ni content. The optical absorption edge of the alloys can be tuned continuously from CdO to NiO. The intrinsic gap of the alloys was calculated with the electrical and optical measurements and accounting for Burstein-Moss carrier filling and carrier-induced bandgap renormalization effects. We observe an uncommon composition dependence of the intrinsic bandgap on the alloy composition. The effect is tentatively attributed to an interaction between extended states of the conduction band and localized d-states of Ni. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4906088] Cadmium oxide is an intriguing n-type wide bandgap

We have grown N-rich, dilute Sb GaN1−xSbx alloys by low temperature molecular beam epitaxy. At low growth temperature of <100 °C the material loses crystallinity and becomes primarily amorphous with small crystallites of 2–5 nm at a Sb composition of >4 at. %. Despite the different microstructures found for GaN1−xSbx alloys with different composition, the absorption edge shifts continuously from 3.4 eV (GaN) to close to 1 eV for samples with Sb content >30 at. %. GaN1−xSbx alloys with less than 5 at. % Sb show sufficient bandgap reduction (∼2 eV), making them suitable for photoelectrochemical applications.

Transparent conductors play an increasingly important role in a number of semiconductor technologies. This paper reports on the defects and properties of Cadmium Oxide, a transparent conducting oxide which can be potentially used for full spectrum photovoltaics. We carried out a systematic investigation on the effects of defects in CdO thin films undoped and intentionally doped with In and Ga under different deposition and annealing conditions. We found that at low growth temperatures (<200 °C), sputter deposition tends to trap both oxygen vacancies and compensating defects in the CdO film resulting in materials with high electron concentration of ∼2 × 1020/cm3 and mobility in the range of 40–100 cm2/V s. Thermal annealing experiments in different ambients revealed that the dominating defects in sputtered CdO films are oxygen vacancies. Oxygen rich CdO films grown by sputtering with increasing O2 partial pressure in the sputter gas mixture results in films with resistivity from ∼4 × 10−4 to >1 Ω cm due to incorporation of excess O in the form of O-related acceptor defects, likely to be O interstitials. Intentional doping with In and Ga donors leads to an increase of both the electron concentration and the mobility. With proper doping CdO films with electron concentration of more than 1021 cm−3 and electron mobility higher than 120 cm2/V s can be achieved. Thermal annealing of doped CdO films in N2 ambient can further improve the electrical properties by removing native acceptors and improving film crystallinity. Furthermore, the unique doping behavior and electrical properties of CdO were explored via simulations based on the amphoteric defect model. A comparison of the calculations and experimental results show that the formation energy of native donors and acceptors at the Fermi stabilization energy is ∼1 eV and that the mobility of sputtered deposited CdO is limited by a background acceptor concentration of ∼5–6 × 1020/cm3. The calculations offer an insight into understanding of the effects of defects on electrical properties of undoped and doped CdO and offer a potential to use similar methods to analyze doping and defect properties of other semiconductor materials.

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SnTe films were deposited by RF magnetron sputtering. The thickness dependence of the sheet hole concentration indicated the presence of a high hole density surface accumulation layer. Irradiation of SnTe by Ne+ ions led to the saturation of the hole concentration corresponding to a Fermi energy that is 0.5 eV below the valence band edge. The stabilized Fermi energy on the surface and in the heavily damaged bulk is in agreement with the amphoteric native defect model. These results show that SnTe is a unique semiconductor with an extremely high valence band edge located at 4.4 eV below the vacuum level.

Articles you may be interested inStructure, band gap, and Mn-related mid-gap states in epitaxial single crystal (Zn1−xMgx)1−yMnyO thin films J. Appl. Phys. 113, 173701 (2013); 10.1063/1.4803141Strain-balanced InAs/InAs1−xSbx type-II superlattices grown by molecular beam epitaxy on GaSb substrates GaN materials alloyed with group V anions form the so-called highly mismatched alloys (HMAs). Recently, the authors succeeded in growing N-rich GaN 1Àx As x and GaN 1Àx Bi x alloys over a large composition range by plasma-assisted molecular beam epitaxy (PA-MBE). Here, they present first results on PA-MBE growth and properties of N-rich GaN 1Àx Sb x and InN 1Àx As x alloys and compare these with GaN 1Àx As x and GaN 1Àx Bi x alloys. The enhanced incorporation of As and Sb was achieved by growing the layers at extremely low growth temperatures. Although layers become amorphous for high As, Sb, and Bi content, optical absorption measurements show a progressive shift of the optical absorption edge to lower energy. The large band gap range and controllable conduction and valence band positions of these HMAs make them promising materials for efficient solar energy conversion devices.