High performance short-wavelength infrared (SWIR) HgCdTe focal plane arrays (FPAs) of 320x256/30μm have been well developed and are now in production at Teledyne Judson Technologies (TJT). These FPAs have two cutoff wavelengths, 2.5μm and 2.9μm in general, and can operate over a wide temperature range. The detector arrays were fabricated primarily with molecular beam epitaxy (MBE) HgCdTe materials, although liquid phase epitaxy (LPE) materials were also used, both materials on CdZnTe substrates. These FPAs use ISC 9809 Si readout integrated circuit (ROIC) and have excellent operability, low dark current, high quantum efficiency (QE), good uniformity and high yield. Comprehensive characterization of FPA performance was performed from room temperature to LN2, and the test results are presented and discussed in this paper. Typical operability is ~99.9%, and peak QE ~85%. FPA noise is background limited at -70°C with field-of-view (FOV) ~100° and becomes lab camera electronics limited when FOV ~0°. Pixel dark current either matches or is below the values from Rule-07 model over a wide temperature range. Noise equivalent irradiance (NEI) of 2-3E9 Ph/cm<sup>2</sup>-s is achieved at -70°C and could be further reduced under smaller FOV.
Teledyne Judson Technologies (TJT) has developed high operating temperature (HOT) mid-wavelength infrared (MWIR) photodetectors based on InAs/InAsSb type-II superlattice (T2SL) with an electron barrier. Large area discrete detectors of 0.25mm and 1mm diameters were designed and fabricated for front-side illumination. Comprehensive E-O characterization was performed at room temperature and thermo-electric cooled (TEC) temperatures. The unique fabrication process was developed for a quasi-planar structure, enabling simplified fabrication for low-cost large volume production. The detector shows a 50% cut-off wavelength of ~5.5μm at room temperature. Peak responsivity of 2.47 A/W was achieved on 1mm detectors at peak wavelength ~ 4.24μm, -0.3V bias and 295K. Peak quantum efficiency (QE) was 72% with an antireflection coating. The 1mm detectors showed peak detectivity (D*) of 1.9x10<sup>9</sup> cm-√Hz/W at -0.3V bias, 295K and 10 kHz. Dark current density as low as 1.17 A/cm<sup>2</sup> was achieved at -0.3V bias and 295K on 1mm detectors. The dark current was diffusion-limited at higher temperatures above ~120K while it was dominated by either tunneling or surface leakage currents at lower temperatures. Similar results were obtained on 0.25mm detectors.
In this paper, we present the test results of a flight-grade 13μm pixel pitch 6000-element 1.7μm InGaAs linear array in a hermetic package, designed and developed for space remote sensing and imaging applications. The array consists of a single 13μm pixel pitch 6000-element InGaAs linear array and a custom single digital 2.0 Mecapacitance trans-impedance amplifier (CTIA) readout integrated circuit (ROIC) with four gains. We have achieved greater than 80% peak quantum efficiency and higher than 1100 signal-to-noise ratio (SNR) at 90% well fill. The focal plane array is in a vacuum hermatically sealed package with an anti-reflective (AR)-coated Sapphire window and 29 pins, including four for low voltage differential signaling (LVDS) outputs.
Teledyne Judson Technologies (TJT) has been developing technology for small pixel, large format, low dark current, and
low capacitance NIR/SWIR InGaAs detector arrays, aiming to produce <10μm pixels and >2Kx2K format arrays that
can be operated at or near room temperature. Furthermore, TJT is now developing technology for sub-10μm pixel arrays
in response to requirements for a variety of low light level (LLL) imaging applications. In this paper, we will review test
data that demonstrates lower dark current density for 10-20μm pixel arrays. We will present preliminary results on the
successful fabrication of test arrays with pixels as small as 5μm. In addition, a lot of effort has been made to control and
reduce the detector pixel capacitance which can become another source of detector noise. TJT is also developing 4"
InGaAs wafer process and now offers four different types of InGaAs 2D arrays/FPAs that are tailored to different
customer requirements for dark current, capacitance, spectral response, and bias range.
This paper reports preliminary results obtained on 1.7µm InGaAs, Vis-InGaAs, extended-wavelength InGaAs, InSb, and HgCdTe 320x256 FPAs fabricated at Judson. Test structures designed to characterize fundamental detector parameters are presented. FPA performance and imaging analysis are reported. Possible performance improvements by means of architectural design and fabrication process refinement are described. Future development plan and preliminary experimental results on FPAs with larger format and smaller pitch are also discussed. Relatively low dark current and NEI values, as well as high operability, are achieved for 1.7µm InGaAs FPAs at room temperature. High quantum efficiency in the visible wavelength range is achieved for Vis-InGaAs FPAs. Low NETD values are achieved for InSb FPAs at LN2 and MWIR HgCdTe FPAs at -70°C (203°K).
A novel InGaAs structure has been developed specifically for use in high-speed applications that require large active
area diodes with greater than 3mm diameter size. The device design is based on a thick and fully depleted PIN structure.
The intrinsic layer thickness is 2 to 4 times thicker than that of the conventional PIN detectors. Greater than 3-fold
reduction in detector capacitance per unit area and the corresponding RC time constant has been demonstrated. Even
with such significant speed enhancement, other diode performance characteristics such as dark current and breakdown
voltage of these novel InGaAs PIN detectors remain comparable to those of the conventional structure. Front- and
backside-illuminated InGaAs detectors are fabricated. Both show equally high-quality spectral response and spatial
uniformity. Comprehensive electro-optical tests are performed and the data and analysis are presented. Temperature
dependent performance characteristics are also reported. Well-behaved performance characteristics are observed from
TE-cooled temperatures to elevated temperatures above ambient.
We report, for the first time, experimental FIR detector results based on p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) structures. The MBE grown samples consist of a multilayer (p<SUP>+</SUP>- p<SUP>-</SUP>-p<SUP>+</SUP>-p<SUP>-</SUP>-...) structure. The detector shows high responsivity over a wide wavelength range with a bias tunable cutoff wavelength ((lambda) <SUB>c</SUB>). Changing the emitter layer (p<SUP>+</SUP>) doping concentration (N<SUB>e</SUB>) will result in different (lambda) <SUB>c</SUB>s. For a detector with N<SUB>e</SUB> equals 3 multiplied by 10<SUP>18</SUP> cm<SUP>-3</SUP>, an effective quantum efficiency of 9.2% (at 26.3 micrometer) with (lambda) <SUB>c</SUB> equals 100 micrometer is obtained. Various experimental results are discussed.
A novel homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared (FIR) detector based on the interfacial workfunction (IWF) between a heavily doped absorber/emitter layer and a lightly doped (or intrinsic) layer is reported. The detector structures are classified according to their emitter layer doping concentrations (N<SUB>d</SUB>). The threshold wavelength ((lambda) <SUB>t</SUB>) is tunable in the IR wavelength range by changing N<SUB>d</SUB> and bias voltage. This detector concept has been successfully demonstrated using forward biased commercial Si and Ge p-i-n diodes at 4.2 K. Threshold wavelengths ((lambda) <SUB>t</SUB>) from around 40 - 220 micrometers for Si and up to 240 micrometers for Ge were experimentally obtained. A theoretical investigation including an estimation of workfunction dependence on N<SUB>d</SUB>, quantum efficiency calculations, and dark current analysis is reported. Based on these results, the detector noise equivalent power (NEP) limited by thermal noise and background noise is calculated.
A study is made of <i>p</i>-type HgCdTe surface passivation with ZnS. Measurements of capacitance-voltage characteristics for metal insulator semiconductor (MIS) devices show that the interface electrical properties strongly depend on the surface preparation. Under some appropriate surface pretreatment, the fixed interface charge density can be lowered to near -1 x 10<sup>11</sup> cm<sup>-2</sup>, and the slow trap density can be less than 1 x 10<sup>11</sup> cm<sup>-2</sup>, but the interface trap density is still as high as 10<sup>12</sup> cm<sup>-2</sup> eV<sup>-1</sup>. Experimental results are discussed.
A theoretical investigation of electrical crosstalk induced by surface channel was made for Hg<SUB>1-x</SUB>Cd<SUB>x</SUB>Te n-on-p photodiode arrays, by using a model based on diode surface channel current theory. An analytic expression of crosstalk, which is an exponential function of the inversion layer charge density, element spacing, p-n junction resistance-area product, and surface electron mobility, was deduced. The dependence of crosstalk on some related device parameters, such as the positive fixed interface charge density, etc., was calculated and discussed. The results show that better control of the substrate surface potential, as well as careful choice of some device parameters, is significant for reducing electrical crosstalk.
Recent developments in HgCdTe photovoltaic detector technology are reviewed. The status of related areas in China are introduced. Some aspects of research work on device physics and technology conducted in the authors' laboratories are discussed. These include: the performance of HgCdTe photodiodes for IR fiber communication; the effects of field- enhanced generation-recombination and imperfections of the pn junction on HgCdTe photodiode I-V characteristics; and an analysis of the dependence of energy gap of HgCdTe on temperature and composition.