Tohru Maekawa

Dislocations in HgCdTe-CdTe and HgCdTe-CdZnTe heterojunctions

Abstract Mechanisms that govern the generation and movement of dislocations in (111) heterojunctions of HgCdTe-CdTe and HgCdTe-CdZnTe grown by liquid phase epitaxy have been investigated with etch pit studies. The density and distribution of the misfit dislocations in these heterojunctions have been measured quantitatively and analyzed to clarify the mechanisms that generated them. The origins of the dislocations threading through the epilayer are also reported.

Preflight test results of the ASTER TIR flight model

The thermal infrared radiometer (TIR) is one of three radiometer on advanced spaceborne thermal emission and reflection radiometer (ASTER) which will be aboard NASAs EOS- AM1 polar orbiting platform to be launched in 1998. TIR will be used for precision observations in various fields, including solid earth science, resources exploration, cloud science, hydrology, and ocean science. Measurements by TIR will be made of surface temperature and emissivity, volcano activity, cloud top temperature, cloud structure, evapotranspiration, and ocean temperature. Manufacturing and testing of the proto-flight model (PFM) has already been done. This paper gives an overview of the proto-flight data based on the proto-flight test (PFT) for the TIR. Major performances are as follows: (1) modulation transfer function (MTF) is larger than 0.25 at Nyquist frequency. (2) Noise equivalent temperature difference (NETD or NE(Delta) T) is less than 0.3 K for 300 K target. (3) Dynamic range is between 200 K and 370 K. The standard blackbody with temperature between 100 K and 400 K was used in vacuum test for NETD, dynamic range and linearity. Also, the collimater was used for MTF and so on. Test has done well and results satisfied with all specifications.

In-flight performance of the ASTER cryocooler

12 The Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) was one of the mission instruments selected by NASA to fly on the EOS-AM1 spacecraft. The EOS- AM1 (Terra) spacecraft was launched from Vandenberg Air Force Base, December 18, 1999. The ASTER consists of a visible and near-infrared radiometer (VNIR), a short-wave infrared radiometer (SWIR) and a thermal infrared radiometer (TIR). Two cryocoolers are required to cool down the infrared detectors for the SWIR and the TIR. Two cold plates act as a heatsink for each compressor unit and maintain in temperature in the range between 20 degree(s)C and 25 degree(s)C by a capillary-pump heat-transfer system (CPHTS). Therefore, environmental temperature conditions are the same for the two compressor units. While the TIR expander unit is thermal controlled by a local radiator with a heat pipe, the SWIR expander unit employs radiative cooling for thermal control. The performance of ASTER cryocooler was evaluation to operate normally, based on the data obtained in the functional checkout in orbit. The SWIR cryocooler cools the detector to the operating temperature of 77 K in the cooldown time of 22 minutes. The TIR cryocooler cools the detector to the operating temperature of 80 K in the cooldown time of 23 minutes. The temperature of each detector was stabilized in the allowable temperature range. A clear image was obtained in the initial checkout of each radiometer in their observation mode.

LATTICE MATCHING IN HgCdTe-CdZnTe HETEROJUNCTIONS

An etch pit study has been made on misfit dislocations in (111) HgCdTe-CdZnTe heterojunctions grown by liquid phase epitaxy. It was shown that misfit dislocations were localized at the original surface of the substrate, because Zn diffused into the epilayer during epitaxial growth prevents movement of dislocations. For lattice matching between Hg 0 7 Cd 0.3 Te and Cd 1−y Zn y Te, the optimum ZnTe mole fraction of Cd 1−y Zn y Te was found to be 2.9%.

Evaluation Method For Infrared Focal Plane Arrays With Metal Insulator Semiconductor (MIS) Structure

This paper describes a new method of surface potential measurement for MIS infrared focal plane arrays. The key feature of this method is a charge sensitive amplifier which detects the surface potential directly. The surface potential is subject to photo-generated charge carriers stored in a potential well as well as the gate voltage. Therefore, this measurement can be used for both electronic and optical characterization of an MIS infrared imager such as an infrared charge coupled device (IRCCD) or an infrared charge injection device (IRCCD). Mercury cadmium telluride (HgCdTe) IRCIDs with 3 x 5 pixels were evaluated using this technique. The measurement was controlled by HP System 35 and proved more accurate, informative, and speedy than the conventional capacitance-voltage (C-V) measurement.

Performance evaluation of ASTER cryocooler in orbit

The advanced spaceborne thermal emission and reflection radiometer (ASTER) was developed by the MInistry of Economy, Trade and Industry (METI) for installation in the EOS-AM1 spacecraft. The ASTER consists of a visible and near-infrared radiometer (VNIR), a short-wave infrared radiometer (SWIR) and a thermal infrared radiometer (TIR). Two cryocoolers are required to cool the infrared detectors for the SWIR and TIR subsystems. Two cryocoolers have been operating in orbit for over 22000 hours. The temperature of each detector was stabilized in the allowable temperature range. Long-term data have been acquired on the cooling performance and power consumption under normal operation for each cryocooler, the following are described; outline of ground test results and performance of the ASTER cryocooler in orbit for over 22000 hours.

Focal plane technology of the thermal infrared radiometer for ASTER

The thermal infrared radiometer (TIR) is one of the three radiometers of the advanced spaceborne thermal emission and reflection radiometer (ASTER). The TIR is a multispectral scanning radiometer for the thermal infrared region of 8 to 12 micrometers. This region is thought to be useful to identify stone and rock classification, investigate clouds, water evaporation, and volcano observation. The TIR and other radiometers are to be loaded to EOS-AM1 polar orbital platform, which is planned to be launched in early 1998 by NASA. At present, developement of the TIR subsystem engineering model has successfully finished and development of the proto-flight model has started. The developemnt of TIR detector has completed attaining high detector performances and high reliability simultaneously, by the developments such as improvements of detector-element structures and improvement of detector/dewar design. In this paper, we report the progres and status of the design and development of the TIR infrared detector.

High Speed Infrared Charge Injecton Device : Design Considerations

This paper describes the results of calculation to develop high speed infrared charge injection devices (IRCIDs). The charge injection time dominates the readout frequency of IRCIDs operated by a sequential injection scheme. The behavior of the injected minority carriers are simulated by solving the diffusion equation. The simulation reveals that the high speed device needs a special structure to eliminate the injected charge. Two devices are proposed. One structure is made on thin n-type layer formed by Hg diffusion to a p-type substrate. The p-n junction underlies the charge storage cell and removes the injected charge. The other structure uses an epitaxially grown substrate and utilizes the HgCdTeCdTe interface as recombination layer of the injected charge.