X-ray Rocking Curve Linewidth Research Articles

Study of the crystalline quality of CdTe, CdZnTe and CdMnTe substrates used for liquid phase epitaxy of Cd 0.7Hg 0.3Te

The crystalline quality of epitaxial layers made of Cd 0.7Hg 0.3Te, which is a very good infrared detector at the optimal transmission wavelength (1.3 μm) in optical fibers, is strongly dependent on the crystalline quality of the substrate. Experimental observations, carried out by means of Berg-Barrett topography, cathodoluminescence, etch-pitting, and X-ray double-crystal rocking curve measurements on several CdTe, Cd 0.96Zn 0.04Te, and Cd 0.9Mn 0.1Te substrates confirm that the addition of Zn results in an improvement of the crystalline quality of the CdTe compound. The best results, in this work, were obtained on Cd 0.96Zn 0.04Te material with an etch-pit density of 5×10 4 cm -2 and an X-ray rocking curve linewidth of 25 arc sec. Mn addition, on the other hand, does not show any change in CdTe crystalline quality. Characterization of Cd 0.7Hg 0.3Te layers grown by liquid phase epitaxy (LPE) on two types of substrates (CdTe, Cd 0.96Zn 0.04Te) has demonstrated the better quality of those epitaxial layers grown on the Cd 0.96Zn 0.04Te substrate. This result constitutes an other indication of the improved crystalline quality of the Cd-rich CdZnTe material.

Molecular-beam epitaxial growth of InSb on GaAs and Si for infrared detector applications

InSb epitaxial films were grown on GaAs and Si substrates by molecular-beam epitaxy using an intermediate AlSb buffer layer. The use of an AlSb intermediate buffer layer greatly facilitates the overgrowth of InSb on significantly lattice-mismatched foreign substrates, such as GaAs and Si. Hall mobility, x-ray rocking curve, and infrared absorption measurements were performed to characterize the samples. Using a 300 nm AlSb buffer layer, 3 μm thick InSb films on GaAs and Si substrates with room-temperature electron mobilities as high as 55 000 cm2 V−1 s−1 were routinely achieved. X-ray rocking curve linewidths of 199 arcsec for InSb on GaAs and 230 arcsec for InSb on Si have been achieved, which represent the best results to date. Our results indicate that AlSb is a very effective buffer layer for InSb devices grown on GaAs and Si substrates.

Electro-Optic Materials by Solid Source MOCVD

AbstractThe solid source MOCVD technique1,2, employing a single powder vaporization source composed of mixed beta-diketonate metalorganic compounds, has been used to grow thin films of a variety of electro-optic materials, including lithium niobate, strontium barium niobate, and potassium niobate. Results for potassium niobate films are quite preliminary, but indicate that a volatile potassium organometallic source can be synthesized which is useful for growing potassium niobate by MOCVD. High quality single phase (001) oriented strontium barium niobate films have been deposited which exhibit waveguiding behavior. The most extensive work has been done on lithium niobate, which has been deposited epitaxially on a variety of substrates. Oriented z-axis (001) films have been grown on c-axis sapphire with and without a (111) oriented platinum base electrode and on a bulk grown lithium niobate substrate. Films grown directly on c-axis sapphire at 700 C exhibit x-ray rocking curve linewidths as low as.044 degrees, nearly perfect in-plane orientation as determined by x-ray phi scans, and peak-to-peak surface roughness less than 40 Å. Optical waveguiding has been demonstrated by a single prism coupling technique on similar films 1175 – 2000 Å thick grown at 500 C, with optical losses of approximately 2 db/cm at 632.8 nm measured over 3.5 cm long films. Polarization vs. electric field measurements on 1100 Å thick films grown on platinum show a hysteresis loop indicating ferroelectric behavior.

Photovoltaic Infrared Devices in Epitaxial Narrow Gap Lead Chalcogenides on Silicon Substrates

ABSTRACTWe review MBE growth of epitaxial IV-VI layers on Si(111) substrates and fabrication of photovoltaic infrared devices in the layers. Cut-off wavelengths are chemically tailored from 3 µm up to above 12 µm by using PbS, PbTe, Pb1−xEuxSe and Pb1−xSnxSe. An intermediate epitaxial stacked CaF2-BaF2 bilayer of 200 nm thickness serves to overcome the large lattice- and thermal expansion mismatch, and device quality IV-VI layers are obtained with layer thicknesses of only 2–4 µm. The layers are untwinned single crystal, exhibit perfectly smooth surfaces with surface defect concentrations down to 103 cm−2, and x-ray rocking curve line-width of ≈150 arcsec. Despite the large thermal expansion mismatch, the (111)-oriented layers withstand multiple cooling cycles down to 15K without problems.Although our IR-device fabrication technique is far from optimized, the sensitivities of our best photovoltaic sensors are comparable to MCT. IV-VI on Si IR sensors have the potential for a low cost technique of large IR focal plane arrays both for the 3–5 µm and 8–12 µm range because of the easy fabrication procedure and because uniformity problems are much less severe in IV-Vls due to the weaker dependence of the band-gap of Pb1−xSnxSe on composition x compared to MCT.

Growth of InGaP on GaAs using gas-source molecular-beam epitaxy

The growth of high-quality InGaP films lattice matched to (100) GaAs substrates by gas-source molecular-beam epitaxy is reported. InxGa1−x P alloys were grown using a P2 molecular-beam produced by thermal decomposition of PH3 at 900 °C in a low-pressure cracking oven, and the composition x was varied from 0.48 to 0.61 using conventional effusion ovens for the In and Ga sources. Sharp (2×1) reflection high-energy electron diffraction patterns were observed during InGaP growth, and smooth surface morphology and a lattice mismatch of <1×10−4 was obtained. Using the optimum growth conditions of a PH3 flow rate of 7.6 standard cm3/min (sccm) and a substrate temperature of ∼490 °C at a growth rate of 0.5 μm/h, InGaP films were found to exhibit low-temperature photoluminesence linewidths as small as 11 meV, x-ray rocking curve linewidths as narrow as 20 arcsec, and electron mobilities similar to that reported for other epitaxial growth techniques.