In situ growth of an ethyl p-hydroxybenzoate single crystal by the vertical Bridgman technique: a potential nonlinear optical material for third-harmonic generation

Optically transparent single crystals of ethyl p-hydroxybenzoate (EPHB) were successfully grown by the vertical Bridgman technique. The crystalline phase and unit-cell dimensions were obtained from powder X-ray diffraction using Rietveld analysis. The presence of defects and grain boundaries was investigated by high-resolution X-ray diffraction. The optical quality of the grown single crystal was assessed by UV–Vis and photoluminescent spectroscopies. A blue emission, with a bi-exponential decay time, was obtained from time-resolved photoluminescence upon laser excitation at 266 nm. The mechanical strength of the EPHB single crystal was studied by Vickers hardness testing. A decrease in the laser-damage threshold was observed with a nanosecond Nd:YAG laser source for increased pulse repetition rates. The third-order nonlinearity, nonlinear absorption coefficient and nonlinear refractive index were measured using the Z-scan technique with a femtosecond Ti:sapphire laser. The third-order nonlinear coefficient values for the grown crystal were compared with those of a potassium dihydrogen phosphate single crystal.

Electrical and photoelectric properties of MoN/p-CdTe and MoN/n-CdTe heterojunctions

Due to the physical properties of MoN and ITO thin films, it was decided to create MoN/p-CdTe and MoN/n-CdTe heterostructures and investigate their electrical and photoelectric properties. The method of reactive magnetron sputtering was used to create thin MoN and ITO films on single crystal CdTe substrates with different conductivity types. To manufacture test heterostructures, the following CdTe crystal substrates were used: 1) p-type conductivity, grown by Bridgman technique at low cadmium vapor pressures; 2) n-type conductivity, grown by Bridgman technique at high cadmium vapor pressures. During the deposition process, the argon pressure in the vacuum chamber was 0.4 Pa. The power of the magnetron was 30 W, the sputtering process continued 5 min at a substrate temperature of 150°C. I-V characteristics of the heterostructures at different temperatures were measured, the height of the potential barrier, the values of the series and shunt resistance were determined. Electrical and photoelectric properties of the heterostructures were studied, and the dominant mechanisms of current transfer at forward displacements was established. The tunnel-recombination mechanism was found to be the dominant mechanism of current transfer in the MoN/p-CdTe and MoN/n-CdTe heterostructures. It was shown that the photoelectric parameters for the MoN/p-CdTe heterostructure are higher than those for MoN/n-CdTe. MoN/p-CdTe heterojunctions have the following photoelectric parameters: open-circuit voltage Voc = 0.4 V, short-circuit current Isc = 24.6 mA/cm2 at an illumination intensity of 80 mW/cm2. This makes them a promising material for the manufacture of detectors of various radiation types.