Heterojunction tunneling field-effect transistors (HTFETs) that use strained-silicon/strained-germanium type-II staggered band alignment for band-to-band tunneling (BBT) injection are simulated using a nonlocal quantum tunneling model. The tunneling model is first compared to measurements of gate- controlled BBT in previously fabricated strained SiGe diodes and is shown to produce good agreement with the measurements. The simulation of the gated diode structure is then extended to study HTFETs with an effective energy barrier of 0.25 eV at the strained-Si/strained-Ge heterointerface. As the band alignment, particularly the valence band offset, is critical to modeling HTFET operation, analysis of measured characteristics of MOS capacitors fabricated in strained-Si/strained-Ge/relaxed Si_0.5Ge_0.5 hetero- junctions is used to extract a valence band offset of 0.64 eV at the strained-Si/strained-Ge heterointerface. Simulations are used to compare HTFETs to MOSFETs with similar technology parameters. The simulations show that HTFETs have potential for low-operating-voltage (V_dd < 0.5 V) application and exhibit steep subthreshold swing over many decades while maintaining high ON-state currents.

Recent advances in the physical vapor deposition (PVD) of protective fluoride films have raised the far-ultraviolet (FUV: 912–1600 Å) reflectivity of aluminum-based mirrors closer to the theoretical limit. The greatest gains, at more than 20%, have come for lithium fluoride-protected aluminum, which has the shortest wavelength cutoff of any conventional overcoat. Despite the success of the NASA FUSE mission, the use of lithium fluoride (LiF)-based optics is rare, as LiF is hygroscopic and requires handling procedures that can drive risk. With NASA now studying two large mission concepts for astronomy, Large UV-Optical-IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission (HabEx), which mandate throughput down to 1000 Å, the development of LiF-based coatings becomes crucial. This paper discusses steps that are being taken to qualify these new enhanced LiF-protected aluminum (eLiF) mirror coatings for flight. In addition to quantifying the hygroscopic degradation, we have developed a new method of protecting eLiF with an ultrathin (10–20 Å) capping layer of a nonhygroscopic material to increase durability. We report on the performance of eLiF-based optics and assess the steps that need to be taken to qualify such coatings for LUVOIR, HabEx, and other FUV-sensitive space missions.

Exciting concepts are under development for flagship, probe class, explorer class, and suborbital class NASA missions in the ultraviolet/optical spectral range. These missions will depend on high-performance silicon detector arrays being delivered affordably and in high numbers. To that end, we have advanced delta-doping technology to high-throughput and high-yield wafer-scale processing, encompassing a multitude of state-of-the-art silicon-based detector formats and designs. We have embarked on a number of field observations, instrument integrations, and independent evaluations of delta-doped arrays. We present recent data and innovations from JPL’s Advanced Detectors and Systems Program, including two-dimensional doping technology, JPL’s end-to-end postfabrication processing of high-performance UV/optical/NIR arrays and advanced coatings for detectors. While this paper is primarily intended to provide an overview of past work, developments are identified and discussed throughout. Additionally, we present examples of past, in-progress, and planned observations and deployments of delta-doped arrays.

We report on the fabrication of metal–dielectric thin film stacks deposited directly onto silicon substrates for use as ultraviolet bandpass filters. Integration of these filters onto silicon improves the admittance matching of the structure when compared to similar designs fabricated on transparent substrates, leading to higher peak transmission or improved out-of-band rejection if used with a Si-based sensor platform. Test structures fabricated with metallic Al and atomic layer deposited ${\mathrm{Al}}_2{\mathrm{O}}_3$ were characterized with spectroscopic ellipsometry and agree well with optical models. These models predict transmission as high as 90% the spectral range of 200–300 nm for simple three-layer coatings.

Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness.

Metallic aluminum mirrors remain the best choice for high reflectance applications at ultraviolet wavelengths (90 to 320 nm) and maintain good performance through optical and infrared wavelengths. Transparent protective coatings are required to prevent the formation of an oxide layer, which severely degrades reflectance at wavelengths below 250 nm. We report on the development of atomic layer deposition (ALD) processes for thin protective films of aluminum fluoride that are viable for application at substrate temperatures $<200°C$. Reflectance measurements of aluminum films evaporated in ultrahigh vacuum conditions, and protected mirrors encapsulated with ALD $AlF3$ are used to evaluate the far ultraviolet (90 to 190 nm) and near ultraviolet (190 to 320 nm) performance of both the ALD material and the underlying metal. Optical modeling is used to predict the performance of optimized structures for future astronomical mirror applications.