Photoluminescence analysis has been implemented to investigate the crystalline properties of Gallium Nitride layers ablated with an XeCl excimer laser. The measurements were carried out on craters up to 1 micrometers deep, which corresponded to almost half the thickness of the deposited film. The craters were etched in an air environment with laser fluences in the range of 99-231 mJ/cm2. In the 350-1200 nm spectral range, the near-band-edge emission, and the donor-acceptor pair recombination were identified. All spectra were dominated by the excitonic recombination. The analysis revealed that during the ablation, the full width at half maximum of the donor-bound luminescence line remained almost independent of both the depth of the crater and of the laser fluence. Also, the donor-acceptor pari recombination, which manifests its presence through a weak yellow luminescence observed in the vicinity of the 600 nm wavelength, has been consistently observed in the spectra. A relative decrease in the excitonic emission indicated that a thin layer of altered material with lower crystalline quality was formed at the surface of the ablated material.
Ablation of indium phosphide wafers in air was performed with 130 fs laser pulses at a wavelength of 800 nm at a low repetition rate of 10 Hz. In order to evaluate the role of the incubation effects, the relationship between the number of laser pulses used for the ablation and the threshold fluence was studied. Particular attention was paid to the chemical composition, surface morphology and structural variations of the ablated area.
The chemical composition and surface morphology of (001) InP wafers, selectively etched in a chlorine atmosphere in the presence of UV laser illumination, was studied. The etching was carried out in a low pressure mixture of chlorine and helium (10% Cl2/He). For etching to take place, the surfaces were exposed to 308 nm pulsed XeCl excimer laser radiation with the fluence well below the ablation threshold of InP. The x-ray photoemission spectroscopy investigations indicate that, at room temperature, the applied etch mixture does not spontaneously react with the InP wafers. Laser irradiation at a fluence less than the ablation threshold of InP stimulates a chemical reaction. At low fluence, no In-Cl compound remains on the wafer surface after the process. In the illuminated areas, the presence of In-P-O and P-O is observed at larger amount than in the non-illuminated areas. Scanning electron microscopy studies show that laser illumination results in the efficient removal of reaction products from the illuminated area. The small scale morphological structures observed on the surface depend on the total amount of exposure to laser radiation.
Laser assisted dry etching ablation of (001) InP wafers in a chlorine atmosphere is studied with spatially resolved x-ray photoelectron spectroscopy (XPS). The etching was carried out in a low pressure mixture of chlorine and helium (10% Cl2 in He). The wafers were exposed to 308 nm pulsed XeCl excimer laser radiation with several values of fluence near the ablation threshold of InP. It was found that, at room temperature, the applied etch mixture does not spontaneously react with the wafer. It was also found that laser irradiation at a fluence less than the ablation threshold of InP stimulates a chemical reaction between the chlorine and the wafer, forming In-Cl compounds. At the same time, the irradiation removes the reaction products.
We discuss optical properties of semiconductor thin films, quantum wells and superlattices grown by pulsed laser deposition. A comparison with semiconductor structures grown by other techniques, such as MBE and CVD, is carried out to evaluate the applicability of laser ablation in the preparation of high quality materials. The discussion is focused on II-VI semiconductor compounds, however other electronic materials, such as CuInSe2 and SiGe, are also briefly mentioned. The emphasis is placed on photoluminescence as the characterization technique.
Multiple quantum wells and superlattices of CdMnTe/CdTe were grown epitaxially on ZnCdTe using Pulsed Laser Evaporation and Epitaxy for Cd.85Mn.15Te doped with indium and high purity CdTe targets. Photoluminescence was measured in the 4-80 K temperature range. The use of different excitation wavelengths (488 nm and 623 nm) led to depth studies of the structures. In order to determine the degree of indium incorporation in the wells, the results from the multiple layer structures were compared with the photoluminescence from single layers deposited under similar conditions.
Multiple quantum wells and superlattices of CdMnTe/CdTe were grown epitaxially on CdZnTe using Pulsed Laser Evaporation and Epitaxy from indium doped Cd.85Mn.15Te and high purity CdTe targets. The photoreflectance and photoluminescence spectra were collected at T equals 5-10 K. In addition to the photoreflectance signatures originating from the CdZnTe substrate, CdTe buffer layer and CdMnTe barrier layers, the spectra also display features that are attributed to optical transitions occurring within the CdTe quantum wells. The signatures were observed in several heterostructures with [001], [111], and [112] crystal orientations.
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