T. L. Lin

Electronic structure of light‐emitting porous Si

Characterization of light‐emitting porous Si films with x‐ray photoelectron spectroscopy is reported. Only traces of O are detected on HF‐etched samples, in contradiction to an earlier report that oxides are a significant component of porous Si. Si 2p and valence‐band measurements demonstrate that the near‐surface region of high porosity films which exhibit visible luminescence consists of amorphous Si.

Hydrogen-terminated silicon substrates for low-temperature molecular beam epitaxy

Abstract The preparation of hydrogen-terminated silicon surfaces for use as starting substrates for low-temperature epitaxial growth by molecular beam epitaxy is examined in detail. The procedure involves the ex-situ removal under nitrogen of residual oxide from a silicon substrate using a spin-clean with HF in ethanol, followed by the in-situ low-temperature desorption (150°C) of physisorbed etch residues. The critical steps and the chemical basis for these steps are examined using X-ray photoelectron spectroscopy. Impurity residues at the epilayer-substrate interface following subsequent homoepitaxial growth are studied using Auger spectroscopy, secondary ion mass spectrometry, and transmission electron microscopy. Finally, scanning tunneling microscopy is used to examine the effect of cleaning methods on substrate morphology.

Novel Si1−xGex/Si heterojunction internal photoemission long‐wavelength infrared detectors

A new approach to the design of a Si‐based infrared detector is demonstrated, based on internal photoemission over a Si1−xGex/Si heterojunction barrier. The heterojunction internal photoemission device structure is grown by molecular beam epitaxy (MBE). The detector requires a degenerately doped p+‐Si1−xGex layer for strong infrared absorption and photoresponse. Doping concentrations to 1020 cm−3 are achieved using boron from a HBO2 source during MBE growth of the Si1−xGex layers. The photoresponse of this device is tailorable, and most significantly, can be extended into the long‐wavelength infrared regime by varying the Ge ratio x in the Si1−xGex layers. Results are obtained with x=0.2, 0.28, 0.3, and 0.4 on patterned Si (100) substrates. Photoresponse at wavelengths ranging from 2 to 10 μm is obtained with quantum efficiencies above ∼1% in these nonoptimized structures.

Microstructural investigations of light-emitting porous Si layers

The structural and morphological characteristics of visible‐light‐emitting porous Si layers produced by anodic and stain etching of single‐crystal Si substrates are compared using transmission electron microscopy and atomic force microscopy (AFM). AFM of conventionally anodized, laterally anodized and stain‐etched Si layers show that the layers have a fractal‐type surface morphology. The anodized layers are rougher than the stain‐etched films. At higher magnification 10 nm sized hillocks are visible on the surface. Transmission electron diffraction patterns indicate an amorphous structure with no evidence for the presence of crystalline Si in the near‐surface regions of the porous Si layers.

9-/spl mu/m cutoff 256/spl times/256 GaAs/Al/sub x/Ga/sub 1-x/As quantum well infrared photodetector hand-held camera

A 9-/spl mu/m cutoff 256/spl times/256 hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated. Excellent imagery, with a noise equivalent differential temperature (NE/spl Delta/T) of 26 mK has been achieved. In this paper, we discuss the development of this very sensitive long wavelength infrared (LWIR) camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NE/spl Delta/T, minimum resolvable temperature (MRTD), uniformity, and operability.

15-{micro}m 128 x 128 GaAs/Al{sub x}Ga{sub 1{minus}x}As quantum well infrared photodetector focal plane array camera

In this paper, we discuss the development of very sensitive, very long wavelength infrared GaAs/Al/sub x/Ga/sub 1-x/As quantum well infrared photodetectors (QWIPs) based on bound-to-quasi-bound intersubband transition, fabrication of random reflectors for efficient light coupling, and the demonstration of a 15-/spl mu/m cutoff 128/spl times/128 focal plane array imaging camera. Excellent imagery, with a noise equivalent differential temperature (NE/spl Delta/T) of 30 mK has been achieved.

Room‐temperature codeposition growth technique for pinhole reduction in epitaxial CoSi2 on Si (111)

A solid phase epitaxy technique has been developed for the growth of CoSi2 films on Si (111) with no observable pinholes (103 cm−2 detection limit). The technique utilizes room‐temperature codeposition of Co and Si in stoichiometric ratio, followed by the deposition of an amorphous Si capping layer and subsequent in situ annealing at 550–600 °C. CoSi2 films grown without the Si cap are found to have pinhole densities of 107–108 cm−2 when annealed at similar temperatures. A CF4 plasma etching technique was used to increase the visibility of the pinholes in the silicide layer. This plasma technique extends the pinhole detection resolution to 103 cm−2 and is independent of the pinhole size.

Intense photoluminescence from laterally anodized porous Si

We have studied photoluminescence (PL) from porous Si anodized laterally along the length of the Si wafer. Broad PL peaks were observed with peak intensities at ∼640 to 720 nm. Strong PL intensity could be observed from 550 to 860 nm. Room‐temperature peak intensities were within an order of magnitude of peak intensities of AlGaAs/GaAs multi‐quantum wells taken at 4.2 K, and total intensities were comparable. A blue shift of peak intensities from ∼680 to 620 nm could be observed after thermal anneal at 500 °C in O2 and subsequent HF dip.

Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p+‐SiGe layers on p−‐Si substrates. Elemental boron from a high‐temperature effusion cell was used as the dopant source during molecular beam epitaxy (MBE) growth, and high doping concentrations (≳5×1020 cm−3) have been achieved. Strong infrared absorption, mainly by free‐carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature (350 °C), resulting in improved crystalline quality and smooth surface morphology of the Si0.7Ge0.3 layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long‐wavelength infrared regime has been demonstrated.

SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy

A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p/sup +/-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17- mu m) regime. Detectors were fabricated by growing p/sup +/-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10/sup 19/ cm/sup -3/ to 4*10/sup 20/ cm/sup -3/. Infrared absorption of 5-25% in a 30-nm-thick p/sup +/-SiGe layer was measured in the 3-20- mu m range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5% have been obtained from test devices in the 8-12- mu m range. >