E. W. Jones

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.

Long-wavelength PtSi infrared detectors fabricated by incorporating a p(+) doping spike grown by molecular beam epitaxy

By incorporating a 1‐nm‐thick p+ doping spike at the PtSi/Si interface, we have successfully demonstrated extended cutoff wavelengths of PtSi Schottky infrared detectors in the long wavelength infrared (LWIR) regime for the first time. The extended cutoff wavelengths resulted from the combined effects of an increased electric field near the silicide/Si interface due to the p+ doping spike and the Schottky image force. The p+ doping spikes were grown by molecular beam epitaxy at 450 °C using elemental boron as the dopant source, with doping concentrations ranging from 5×1019 to 2×1020 cm−3. Transmission electron microscopy indicated good crystalline quality of the doping spikes. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p+ spikes. Thermionic emission dark current characteristics were observed and photoresponses in the LWIR regime were demonstrated.

Photoresponse model for Si/sub 1/spl minus/x/Ge/sub x//Si heterojunction internal photoemission infrared detector

A photoresponse model has been developed for the Si/sub 1/spl minus/x/Ge/sub x//Si heterojunction internal photoemission (HIP) infrared detector at wavelengths corresponding to photon energies less than the Fermi energy. A Si/sub 0.7/Ge/sub 0.3//Si HIP detector with a cutoff wavelength of 23 /spl mu/m and an emission coefficient of 0.4 eV/sup /spl minus/1/ has been demonstrated. The model agrees with the measured detector response at /spl lambda/>8 /spl mu/m. The potential barrier determined by the model is in close agreement (difference /spl sim/4 meV) with the potential barrier determined by the Richardson plot, compared to the discrepancies of 20-50 meV usually observed for PtSi Schottky detectors.<<ETX>>

Doping-spike PtSi Schottky infrared detectors with extended cutoff wavelengths

A technique incorporating a p/sup +/ doping spike at the silicide/Si interface to reduce the effective Schottky barrier of the silicide infrared detectors and thus extend the cutoff wavelength has been developed. In contrast to previous approaches which relied on the tunneling effect, this approach utilizes a thinner doping spike ( >

Long‐wavelength stacked SiGe/Si heterojunction internal photoemission infrared detectors using multiple SiGe/Si layers

Utilizing low temperature silicon molecular beam epitaxy growth, long‐wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Si layers have been fabricated and demonstrated. Using an elemental boron source, high doping concentration (≊4×1020 cm−3) has been achieved and high crystalline quality multiple Si0.7Ge0.3/Si layers have been obtained. The detector structure consists of several periods of degenerately boron doped (≊4×1020 cm−3) thin (≤50 A) Si0.7Ge0.3 layers and undoped thick (≊300 A) Si layers. The multiple p+‐Si 0.7Ge0.3/undoped‐Si layers show strong infrared absorption in the long‐wavelength regime mainly through free‐carrier absorption. The stacked Si0.7Ge0.3/Si HIP detectors with p=4×1020 cm−3 exhibit strong photoresponse at wavelengths ranging 2–20 μm with quantum efficiencies of about 4% and 1.5% at 10 and 15 μm wavelengths, respectively. The detectors show near ideal thermionic‐emission limited dark current characteristics.

7-μm-cutoff PtSi infrared detector for high sensitivity MWIR applications

PtSi Schottky infrared detectors with extended cutoff wavelengths of 5.7, 6.6, and 7.3 /spl mu/m have been demonstrated by incorporating a thin p+ layer at the PtSi-Si interface for high sensitivity medium wavelength infrared imaging applications. The response uniformity of the 7-/spl mu/m cutoff detector was studied.<<ETX>>

Infrared photodetectors with tailorable response due to resonant plasmon absorption in epitaxial silicide particles embedded in silicon

Photodiodes with epitaxial CoSi2 particles embedded in a single‐crystal silicon matrix show response in the 1–2 μm range with structure which correlates with absorption peaks due to the surface plasmon resonance of the particles. Aspect ratios (height:diameter) of the particles are accurately controlled by molecular beam epitaxy over a range from 1.4:1 to 1:7, allowing the absorption peaks to be tailored from 1.2 to 2.6 μm, respectively. The particle surface plasmon excitation modifies the photoresponse of the devices and allows this response to be tailored through control of the dimensions of the particles. The photodiodes were tested at 77 K, and 4 of 8 devices tested with an absorption peak at 1.7 μm show dark currents less than 2 nA/cm2 at a reverse bias of 1 V. Detectivities for the same devices at 77 K range from 4×109 to 8×109 cm√Hz/W.

Tailorable Doping-Spike PtSi Infrared Detectors Fabricated by Si Molecular Beam Epitaxy

By incorporating a 1-nm-thick p+ doping spike at the PtSi/Si intertace, we have successfully demonstrated extended cutoff wavelengths of PtSi Schottky infrared detectors. The extended cutoff wavelengths resulted from the reduced effective potential barriers due to the combined effects of an increased electric field near the silicide/Si intertace and the Schottky image force. The p+ doping spikes were grown by molecular beam epitaxy at 450° C using elemental boron as the dopant source, with doping concentrations ranging from 5×1019 to 2×1020 cm-3. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p+ spikes. Thermionic emission dark current characteristics were observed and photoresponse in the LWIR regime was demonstrated. Furthermore, the effective potential barriers determined by the Richardson plots were used to study the electrically activated boron dopant concentrations of the thin (1-nm-thick) spikes.

Proton irradiation effects on strained Si1−xGex/Si heterostructures

Proton irradiation effects on strained Si1−xGex/Si heterostructures have been studied. For the experiment, p+‐Si1−xGex/p−‐Si heterojunction diodes were fabricated by molecular beam epitaxy (MBE) growth of strained p+‐boron doped SiGe layers on p−‐Si(100) substrates. Due to the valence band discontinuity between SiGe and Si layers, and degenerate doping in the SiGe layer, the characteristics of these heterojunction diodes are similar to those of metal‐semiconductor Schottky barrier diodes. The SiGe/Si heterojunction diodes are irradiated by 1 Mrad of protons at 1 and 8.5 MeV energies. The current‐voltage (I‐V) characteristics are measured as a function of temperature before and after irradiation. I‐V characteristics show a decrease of the reverse bias leakage current after irradiation. The effective heterojunction barrier heights (Φb) and Richardson constants (A**) are measured before and after irradiation using activation energy measurements. The measurements show an increase of Φb and A** after irradiati...

Novel Si‐based superlattices consisting of alternating layers of crystalline Si and porous amorphous Si1−xGex alloys

Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si1−xGex have been studied. These are fabricated by immersing mesa structures of molecular‐beam‐epitaxy grown Si/Si0.7Ge0.3 superlattices in an HF:HNO3:H2O solution. A high selectivity in the pore formation leads to lateral penetration of pores ≊0.7 μm into 5‐nm‐thick Si0.7Ge0.3 layers. The effect of the etch on layers with differing alloy composition, thickness, and strain has been examined. Homogeneous strain has been identified as an important factor in establishing the selectivity of the etch, but other factors clearly play important roles as well.