Real-time Temperature Compensation Research Articles

Growth and characterization of AgGa1−xInxSe2 crystals with high indium contents

Large, integral AgGa1−xInxSe2 (x=0.6, 0.8) single crystals were grown from a melt. The polycrystalline charges were successfully synthesized from high purity elemental starting materials by the vapor transport method with the melt and temperature oscillation. The crystallization processes were carried out in two-layer quartz ampoules with ampoule rotation and the real-time temperature compensation technique. The quality of the as-grown crystals was characterized using a microscope, XRD, IR and vis–NIR spectrophotometers, etc. Cleavage faces of (112) were found, and high transmittance of the crystals in the mid-near IR region was revealed. The absorption edges of the materials are near 905 and 958nm, and the calculated band gaps are about 1.37 and 1.29eV. All the measurements confirmed the good quality of the grown crystals.

Real-Time Temperature Compensation of MEMS Oscillators Using an Integrated Micro-Oven and a Phase-Locked Loop

We present a new temperature compensation system for microresonator-based frequency references. It consists of a phase-locked loop (PLL) whose inputs are derived from two microresonators with different temperature coefficients of frequency. The resonators are suspended within an encapsulated cavity and are heated to a constant temperature by the PLL controller, thereby achieving active temperature compensation. We show repeated real-time measurements of three 1.2-MHz prototypes that achieve a frequency stability of ± 1 ppm from -20°C to +80°C, as well as a technique to reduce steady-state frequency errors to ±0.05 ppm using multipoint calibration.

Improved growth and characterization of AgGa 1−xIn xSe 2 crystals

Good quality AgGa 1− x In x Se 2 ( x=0.1–0.3) single crystals with 20 mm diameter and 60 mm length have been grown by an improved Bridgman method, i.e. descending ampoule with rotation and the real-time temperature compensation technique. The melt temperature oscillation method (MTOM) was used to synthesize high-purity single-phase AgGa 1− x In x Se 2 polycrystal that is free of voids. The crystallization process was carried out in the two-layer quartz ampoule with a seed pocket. The temperature gradient at the growth interface in the furnace was normally 20 °C cm −1 in the open bore, while it was 15 °C cm −1 with the ampoule in the furnace. The quality of the as-grown crystal was characterized by using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), infrared (IR) spectrophotometer, etc. It was found that there is a {1 1 2} cleavage face in the as-grown crystal and the homogeneous growth steps on the {1 1 2} face were observed. The four-order diffraction peaks of the {1 0 1} faces were evident. The transmittance of the crystal sample of 2 mm thickness is up to 65% in the region of 700–6500 cm −1. The results demonstrated that the improved new growth method of AgGa 1− x In x Se 2 single crystals is promising and the quality of the grown crystals is good, and after annealing, the crystals can be used for IR nonlinear optical devices.

Growth and characterization of ZnGeP 2 single crystals by the modified Bridgman method

A good quality ZnGeP 2 (ZGP) single crystal 15 mm in diameter and 40 mm in length was grown in a vertical three-zone tubular furnace by the modified Bridgman method, i.e. real-time temperature compensation technique (RTTCT) with descending ampoule. The starting material is high-pure and single-phase polycrystal of ZnGeP 2 synthesized by the single-temperature zone and mechanical oscillation method (STZMOM). The as-grown single crystal was characterized by various methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analyzer of X-ray (EDAX), and IR and UV spectrophotometers. It is found that there is a cleavage face of (1 1 2) and second-order XRD peaks of the {1 1 2} faces are observed, the IR transmittance of a sample of 2 mm thickness is above 55% in the range from 6000 to 800 cm −1, the absorption edge is near 612.5 nm and the band gap is about 2.02 eV. The absorption coefficient ( α) is within 0.015–0.022 cm −1 at the spectral region 2–8 μm. The crystal has a stoichiometry ratio Zn:Ge:P=1:1.12:1.91 which is close to the ideal stoichiometry ratio of 1:1:2. All results demonstrate that the modified growth method is a new and promising method for the ZGP single crystal and the quality of as-grown crystal is good.