The concept of homojunction infernal photoemission far-infrared (FIR) detectors has been successfully demonstrated using forward biased Si p-in diodes at 4.2 K. The basic structure consists of a heavily doped IR absorber layer and an intrinsic (or lightly doped) layer. An interfacial workfunction between these regions defines the long-wavelength cutoff (X,) of the detector. Three types of detectors are distinguished according to the emitter layer doping concentration level. Our model shows that high performance Si FIR detectors (>40 pm) can be realized using the type-II structures with a tailorable X,, in which the absorber/emitter layer is doped to a level somewhat above the metal-insulator transition value. Analytic expressions are used to obtain the workfunction versus doping concentration, and to describe the carrier photoemission processes. The photoexcitation due to free-carrier absorption, emission to the interfacial barrier, hot-carrier transport, and barrier collection due to the image force effect, are considered in calculating the spectral response and quantum efficiency as functions of device parameters for Si n+ '-1 structures, leading to a detailed photoresponse analysis of type-II detectors. These results are useful for the design and optimization of type-II detectors.

A molecular beam epitaxy grown wavelength tunable GaAs p ϩ -i homojunction interfacial work-function internal photoemission far-infrared detector is developed. The multilayer ( p ϩ -ip ϩ -i-. . . ͒ detector structures consist of 2, 5, and 10 emitter layers. Experimental results are explained in terms of the number of emitter layers and the doping concentrations of the emitter layer. A detector with 10 multilayers and an emitter layer doping concentration (N e ) of 3ϫ10 18 cm Ϫ3 shows a current responsivity of 2 A/W, an effective quantum efficiency of 9.2% ͑at 26.3 m͒ with a cutoff wavelength of 85 m and the noise equivalent power of 2.18ϫ10 Ϫ12 W/ͱHz at 4.2 K.

We investigate the nonlinear optical response of a commercial extended-wavelength In 0.81 Ga 0.19 As photodetector. Degenerate two-photon absorption in the mid-infrared range is observed at room temperature using a quantum cascade laser emitting at λ = 4.5 µm as the excitation source. From the measured two-photon photocurrent signal we extract a two-photon absorption coefficient β (2) = 0.6 ± 0.2 cm/MW, in agreement with the theoretical value obtained from the E −3 g scaling law. Considering the wide spectral range covered by extended-wavelength In x Ga 1−x As alloys, this result holds promise for new applications based on two-photon absorption for this family of materials at wavelengths between 1.8 and 5.6 µm.

A detailed theoretical investigation of dark current mechanisms is performed for a novel Si n+-i homojunction interfacial work function internal photoemission (HIWIP) far-infrared (FIR) detector. Thermionic emission, thermionic field emission and field emission currents, including the image force effect, are calculated and compared as functions of bias voltage and temperature. The bias and temperature dependence of detector noise equivalent power (NEP), limited by thermal noise and background noise, is also calculated. From these results, the optimal operating temperatures and bias voltages are determined. Results show that Si HIWIP FIR detectors may have a performance comparable to the conventional Ge FIR detectors, with some unique advantages over them.

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 LN 2 and MWIR HgCdTe FPAs at -70°C (203°K).