Michael J. Estes

Macroelectronics: Perspectives on Technology and Applications

Flexible, large area electronics - macroelectronics - using amorphous silicon, low-temperature polysilicon, or various organic and inorganic nanocrystalline semiconductor materials is beginning to show great promise. While much of the activity in macroelectronics has been display-centric, a number of applications where macroelectronics is needed to enable solutions that are otherwise not feasible are beginning to attract technical and/or commercial interest. In this paper, we discuss the application drivers and the technology needs and device performance requirements to enable high performance applications to include RF systems.

Traveling-Wave Metal/Insulator/Metal Diodes for Improved Infrared Bandwidth and Efficiency of Antenna-Coupled Rectifiers

We evaluate a technique to improve the performance of antenna-coupled diode rectifiers working in the IR. Efficient operation of conventional, lumped-element rectifiers is limited to the low terahertz. By using femtosecond-fast MIM diodes in a traveling-wave (TW) configuration, we obtain a distributed rectifier with improved bandwidth. This design gives higher detection efficiency due to a good match between the antenna impedance and the geometry-controlled impedance of the TW structure. We have developed a method for calculating the responsivity of the antenna-coupled TW detector. Three TW devices, made from different materials, are simulated to obtain their impedance and responsivity at 1.5, 3, 5, and 10 μm wavelengths. The characteristic impedance of a 100-nm-wide TW is in the range of 50 Ω and has a small variation with frequency. A peak responsivity of 0.086 A/W is obtained for the Nb-Nb2 O5 -Nb TW diode at 3-μm wavelength. This corresponds to a quantum efficiency of 3.6% and is a significant improvement over the antenna-coupled lumped-element diode rectifiers. For IR imaging, this results in a normalized detectivity of 4 × 106 Jones at 3 μm. We have identified several ways for improving the detectivity of the TW detector. Possible methods include decreasing the diode resistance, reducing the noise, and increasing the effective antenna area.

A model of size‐dependent photoluminescence in amorphous silicon nanostructures: Comparison with observations of porous silicon

We present calculations using a simple model of radiative recombination in 2D slabs, 1D wires, and 0D spheres of hydrogenated amorphous silicon (a‐Si:H) showing a significant size dependence of the photoluminescence. Room‐temperature peak emission energies ≳1.8 eV and efficiencies near unity are possible in a‐Si:H spheres with diameters <20 A. Broad homogeneous linewidths ≳0.25 eV are also predicted for these highly confined structures. While the effects are similar to those predicted from quantum confinement, these results are caused by the statistics of spatial confinement. We suggest that these results provide insights into nanostructured a‐Si:H structures and porous silicon.

Visible photoluminescence from porous a-Si:H and porous a-Si:C:H thin films

We report on the influence of doping, temperature, porosity, band gap, and oxidation on the photoluminescence (PL) properties of anodically etched porous a-Si:H and a-Si:C:H thin films. Only boron-doped, p-type a-Si:H samples exhibited visible photoluminescence. Two broad PL peaks at ∼1.6 and ∼2.2 eV are apparent in room temperature PL spectra. The intensity of the 2.2 eV peak as well as the nanovoid density in the unetched a-Si:H layers both correlate well with boron concentration. We see evidence of discrete defect or impurity levels in temperature-dependent luminescence measurements, where we observe multiple luminescence peaks. Unlike in porous crystalline silicon, the luminescence energy in porous amorphous silicon does not change with porosity. We do, though, observe a correlation of luminescence energy with band gap of the starting a-Si:C:H films. Oxidation, either native or anodic, reduces photoluminescence intensity. We discuss the implications of these observations on the nature of the luminesce...

Characterization of the visible photoluminescence from porous a-Si:H and porous a-Si:C:H thin films

The authors report on the influence of doping, temperature, porosity, and bandgap on the visible photoluminescence properties of anodically-etched porous a-Si:H and a-Si:C:H thin films. Only boron-doped, p-type a-Si:H or a-Si:C:H samples exhibited any visible photoluminescence. The authors see evidence of discrete defect or impurity levels in temperature-dependent luminescence measurements. Unlike in porous crystalline silicon, they see no correlation of luminescence energy with porosity. The authors do, though, observe a correlation of luminescence energy with bandgap of the starting a-Si:C:H films. They discuss the implication of these observations on the nature of the luminescence mechanism.