ZnTe Homoepitaxial Layers Research Articles

Low pressure MOVPE growth and characterization of ZnTe homoepitaxial layers

AbstractThe growth rate and photoluminescence (PL) spectrum of ZnTe homoepitaxial layer grown at a reactor pressure of 500 Torr by metalorganic vapor phase epitaxy have been clarified as a function of substrate temperature. An optimum substrate temperature for obtaining ZnTe layers with better PL property is determined by taking into account the growth rate behavior. Furthermore, the growth rate, PL spectrum, surface roughness and surface morphology of ZnTe layer have also been investigated by varying reactor pressure. With increasing reactor pressure, both the PL property and surface roughness of ZnTe layer are improved and subsequently become degraded, according as the growth rate increases monotonically and then shows saturated tendency. Change in the surface morphology of ZnTe layer with the increase of reactor pressure resembles that with the decrease of substrate temperature, probably due to the change from mass‐transport regime to surface kinetics one. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Post-annealing effect upon electrical and optical properties of MOVPE grown P-doped ZnTe homoepitaxial layers

The effect of post-annealing treatment upon the electrical and optical properties of phosphorus-doped ZnTe homoepitaxial layers grown by metalorganic vapour phase epitaxy using tris-dimethylaminophosphorus (TDMAP) has been investigated. After the annealing treatment in N2 atmosphere, all the layers exhibited not only improvement of the optical properties but also enhancement of the carrier concentration by one order. Almost linear relationship between the carrier concentration and transport rate of TDMAP is obtainable by the post-annealing treatment. The reversible change of PL properties by alternate annealing treatment in H2 and in N2 was also revealed.

Post‐annealing effect upon phosphorus‐doped ZnTe homoepitaxial layers grown by MOVPE

AbstractThe effect of post‐annealing treatment upon the photoluminescence (PL) spectra of phosphorus‐doped ZnTe homoepitaxial layers grown by metalorganic vapour phase epitaxy using tris‐dimethylaminophosphorus (TDMAP) has been investigated. PL properties at 4 K of the layers are dramatically improved by the post‐annealing in nitrogen flow, i.e. donor–acceptor pair emission vanishes and instead free‐to‐bound transition emission (FB) and broadened acceptor‐related excitonic emission (Ia) appear. PL intensity at room temperature is enhanced remarkably by the treatment. While the post‐annealing treatment in hydrogen flow also gives an increase in PL intensity at room temperature of the layer, PL spectrum at 4 K is almost unchanged. The intensity ratio of FB to broadened Ia for the layer after post‐annealing treatment in nitrogen flow increases and the broadened Ia shifts towards longer wavelength side with increasing TDMAP transport rate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence of Cl-doped ZnTe epitaxial layer grown by atmospheric pressure metalorganic vapor phase epitaxy

Effects of Cl doping on the photoluminescence (PL) of ZnTe homoepitaxial layers grown by atmospheric pressure metalorganic vapor phase epitaxy using n-butylchloride (n-BuCl) have been investigated. A quite strong donor bound excitonic emission was observed by increasing the n-BuCl transport rate, implying that Cl is incorporated into ZnTe layer as a donor. From the temperature dependence of PL spectra, the thermal activation energy of donor bound excitonic emission was found to be 5.9 meV. Two luminescence bands due to donor-acceptor pair emission appeared at 2.34 and 2.22 eV in the layer grown at an n-BuCl transport rate as high as 0.2 μmol/min. The donor and acceptor levels corresponding to the PL peak at 2.34 eV were estimated to be 22 and 51 meV from the excitation power dependence of PL peak energy, respectively.

Low temperature treatment of the (001) ZnTe substrate surface with the assist of atomic hydrogen

Recent success in the fabrication of the bulk ZnTe has enabled the realization of large area single crystal substrates. The growth and application of ZnTe homoepitaxial layers by molecular beam epitaxy should involve the pretreatment of the substrate surface prior to the nucleation. An atomic hydrogen treatment was performed to remove the surface oxide of ZnTe. The oxide could be removed at around 100 °C with the assist of the atomic hydrogen beam. The reconstructed surface could be achieved by annealing at around 230 °C. The two dimensional nucleation was also confirmed. The homoepitaxial layer has shown such a high quality that interface, or defects could not be confirmed by the transmission electron microscopy.

Photoluminescence of iodine-doped ZnTe homoepitaxial layer grown by metalorganic vapor phase epitaxy

Photoluminescence (PL) properties of I-doped ZnTe homoepitaxial layers grown by atmospheric pressure metalorganic vapor phase epitaxy have been investigated as a function of n-butyliodide (n-BuI) transport rate. The PL spectrum changed drastically even when a low dopant transport rate was used. A structured emission band at 2.22 eV was detected predominantly at low n-BuI transport rates, whereas a structureless broad emission band at around 2.17 eV or less dominates the PL spectrum at high n-BuI transport rates. PL spectra of I-doped ZnTe layers were analyzed at varying excitation power and temperature. These luminescence bands are due to donor–acceptor pair recombination, and may be ascribed to complexes consisting of Zn vacancies and I on Te sites close to donors.

Growth and optical properties of high-quality ZnTe homoepitaxial layers by metalorganic vapor phase epitaxy

Homoepitaxial growth of ZnTe layers have been investigated by changing the total gas flow rate in a metalorganic vapor phase epitaxial system using a horizontal reactor. Correlations between the growth process and the photoluminescence properties of the layers have been clarified. A high-quality ZnTe homoepitaxial layer with strong free excitonic emission was obtained in this experiment. The binding energy of the free exciton and the temperature dependence of the band gap has been investigated using this sample. The resistivity of a sample was estimated to be as high as 5×10 8 Ω cm supporting a high-quality epitaxial layer.

Photoluminescence properties of ZnTe homoepitaxial layers grown by synchrotron-radiation-excited growth using nitrogen carrier gas

ZnTe homoepitaxial layers have been grown by synchrotron-radiation-excited growth using diethylzinc and diethyltelluride with nitrogen carrier gas. Effects of carrier gas on the growth rate and photoluminescence (PL) properties of the ZnTe layers have been investigated. No remarkable difference was found in the growth rate of the deposited layer between hydrogen and nitrogen carrier gases at low substrate temperature up to 60 °C. However, at high substrate temperature, the growth rate obtained using nitrogen carrier gas exhibits only a slight reduction, while that using hydrogen is significantly reduced. PL spectra exhibit a sharp excitonic emission at 2.375 eV associated with shallow acceptor in the ZnTe layer grown under the condition of various VI/II ratios and substrate temperature condition by using nitrogen carrier gas, different from the case of hydrogen carrier gas.

Structural and optical properties of high-quality ZnTe homoepitaxial layers

The structural and optical properties of high-quality homoepitaxial ZnTe films are investigated. A substrate surface treatment using diluted HF solution plays a key role in growing device-quality ZnTe layers. X-ray diffraction analysis of ZnTe epilayers based on the crystal-truncation-rod method suggests that a homoepitaxial ZnTe film grown on a HF-treated substrate can be regarded as an ideal truncated crystal without an interfacial layer, while a ZnTe layer grown on a substrate without HF treatment suggests the presence of an interfacial layer which may lead to degraded crystallinity of ZnTe overlayers. The crystal quality of the homoepitaxial ZnTe layers with HF treatments are characterized by an extremely narrow x-ray diffraction linewidth of 15.6 arcsec and dominant very sharp excitonic emission lines with dramatically reduced deep-level emission intensity in the photoluminescence (PL) spectrum. Three bound excitonic emission lines at neutral acceptors are observed in the PL from the high-quality ZnTe homoepitaxial layers in addition to the free-exciton emission line, suggesting the presence of three different kinds of residual acceptor impurities.

Low-pressure MOCVD growth of ZnTe and observation of gas reaction

ZnTe homoepitaxial layers have been grown as a function of the transport rate of source materials by metalorganic vapor phase deposition method. The growth rate increases sublinearly with increasing the transport rate of diethyltelluride (DETe), while it shows a maximum with the transport rate of dimethylzinc (DMZn). The surface of the layer grown on the (110) or (100) faces becomes smooth as the transport rate of DETe increases. From the quadrupole mass spectra, a dominant reaction product is CH 4 at the high transport rate of DMZn, indicating that a large amount of methyl radicals is formed. The behavior of the growth rate is qualitatively explained with the Langmuir-Hinshelwood model, in which these radicals occupy the surface sites.

Photoluminescence of ZnTe homoepitaxial layers grown by metalorganic vapor-phase epitaxy at low pressure

Photoluminescence (PL) spectra have been investigated at liquid-He temperature in the ZnTe layers grown by metalorganic vapor-phase epitaxy. The epitaxial layer exhibits the spectra characterized by a neutral acceptor bound-exciton line in the near-band edge and the donor-acceptor pair emission in the wavelength range of 550–580 nm. At the low substrate temperature or low transport rate ratio of diethyltelluride to dimethylzinc, the spectrum of layer becomes dominated by this donor-acceptor pair emission. From the results of secondary-ion mass spectrometry analysis and PL property, it is concluded that Na and Cl are important impurities in the layer.