Semiconductor Material For Use Research Articles

Characterization of copper indium ditelluride/electrolyte interface utilizing electrochemical impedance spectroscopy

Copper indium telluride (CIT) is a promising semiconductor material for use in thin film solar cells, especially photoelectrochemical solar cells (PESC). Impedance measurements were used to evaluate the relative band edge positions of polycrystalline n-CuInTe 2 electrodes in various aqueous electrolytes, by measuring the extrapolated flat-band potentials, V fb. By varying applied dc potential, frequency and pH of the electrolyte, the semiconductor–electrolyte interfaces are studied through capacitance measurements and Mott–Schottky analysis. The flat-band potential and carrier concentrations were determined from the Mott–Schottky plots. It was found that V fb could be shifted depending on the pH of the electrolyte, while it is independent of the testing frequency. The changes in V fb with pH could be due to surface states and other modifications through etching and polishing. The surface carrier concentrations were found to increase with pH. The different surface chemistry studied by X-ray photoelectron spectroscopy might account for this change.

Electronic noise in lead iodide X-ray detectors

Lead iodide (PbI 2) is a wide bandgap semiconductor ( E g = 2.32 eV) and has been studied over the past several years as a semiconductor material for use in solid state X-ray and gamma-ray detectors. Small lead iodide detectors have been found to operate with low noise and good energy resolution (500 eV FWHM for 5.9 keV 55Fe X-rays). In the interest of reducing the electronic noise in lead iodide detection systems we have characterized the measured noise in the lead iodide detectors, and have compared the measurements with known noise models. It has been assumed that the noise sources in the lead iodide detectors would take form of a combination of series thermal noise, detector shot noise, and 1 ƒ noise. Detectors with differing areas and thicknesses were analyzed by measuring their noise as a function of the amplifier integration time. A computer fitting program was used to obtain the magnitude of each noise source. Based on this analysis, 1 ƒ noise was found to be the dominant noise source in most detectors at larger integration times of 4 μs to 12 μs, in which range the detectors are normally operated. The 1 ƒ noise was also found to be proportional to the input capacitance, indicating that it is dominated by the series 1 ƒ noise. The 1 ƒ noise magnitude appears to be dependent on the detector fabrication procedures, and may be reduced in future detectors by using more suitable fabrication procedures.

Citric Acid Etching of GaAs1 − xSbx, Al0.5Ga0.5Sb , and InAs for Heterostructure Device Fabrication

Citric acid/hydrogen peroxide at volume ratios from 0.2:1 to 20:1 was found to provide selective etching between , , , and various III–V semiconductor materials for use in new and based heterostructure transistors and optoelectronic devices. By choosing different concentration volume ratios of citric acid to hydrogen peroxide , highly selective as well as uniform (nonselective) etching regions were found to exist in these material systems. Etchant selectivities greater than 50 were found for most combinations of the III–V semiconductor materials under investigation, with selectivities of over 100 measured for and material combinations, and with selectivities of over 3850 calculated for to 13,650 for . The highest overall etch rates were measured for and the lowest etch rates were found for . The etch rate for the materials systematically decreased from the highest etch rate for the smallest Sb mole fraction examined of to the lowest etch rate for . The dramatic change in etch rate with citric acid/hydrogen peroxide volume ratio previously observed for the material system was also observed for , but this effect was not seen in higher Sb mole fraction alloys of examined. and were found to have very low etch rates with this etchant system at all volume ratios, making both materials suitable as an etch stop layer for simplified processing in device fabrication. Finally, citric acid/hydrogen peroxide can be used to preferentially etch these materials through a photoresist mask, since it does not erode photoresist at any volume ratio.