Herman A. Lopez

Erbium emission from porous silicon one-dimensional photonic band gap structures

We report tunable, narrow, directional, and enhanced erbium emission from one-dimensional photonic band gap structures. The structures are prepared by anodic etching of crystalline silicon and consist of two highly reflecting porous silicon Bragg reflectors sandwiching an active layer. The cavities are doped by cathodic electromigration of the erbium ions into the porous silicon matrix, followed by high temperature oxidation. By controlling the oxidation temperature of the structure, the position of the erbium emission near 1.5 μm is tuned to regions where the natural erbium spectrum is very weak. The erbium emission from the cavity is narrowed to a full width at half maximum of 12 nm with a quality factor Q of 130, highly directional with a 20° emission cone around the normal axis, and enhanced by more than one order of magnitude.

Porous silicon multilayer structures: A photonic band gap analysis

A photonic model for freshly anodized porous silicon multilayer structures is presented. The photonic structures are composed of alternating high and low dielectric function porous silicon layers. The model takes into account the presence of silicon dioxide and its lattice expansion in the porous structure. We work with oxidized structures and our results fit completely the experimentally measured optical shift.

Infrared LEDs and microcavities based on erbium-doped silicon nanocomposites

Abstract We demonstrate stable room-temperature electroluminescence at 1.54 μm under both forward and reverse bias conditions from erbium-doped silicon nanocomposites. We also show enhanced and tunable emission from erbium when incorporated in porous silicon based microcavities. Erbium is infiltrated in the pores by cathodic electrochemical migration of the ions followed by high temperature annealing (600–1100°C) to produce a composite material made of silicon nanocrystals and silicon dioxide. The devices exhibit an exponential electroluminescence dependence in both bias conditions as a function of the driving current and driving voltage. In reverse bias, the external quantum efficiency reaches 0.01%. The devices show a large temperature dependence of the electroluminescence intensity. The electroluminescence intensity decreases by a factor of 24 in reverse bias and 2.6 in forward bias when the temperature increases from 240 to 300 K. The photoluminescence from the erbium-doped microcavity resonators is enhanced by more than one order of magnitude and tuned to emit in areas where the natural erbium emission is very weak.

Room-temperature electroluminescence from erbium-doped porous silicon

We demonstrate stable room-temperature electroluminescence (EL) at 1.54 μm from erbium-doped porous silicon devices under both forward- and reverse-bias conditions. Erbium was infiltrated in the pores (⩽1019 cm−3) by cathodic electrochemical migration of the ions followed by high-temperature annealing (950–1100 °C) in an oxygen and nitrogen environment. The devices exhibit an exponential EL dependence in both bias conditions as a function of input power. In reverse bias, the external quantum efficiency reaches 0.01%. The EL intensity decreases by a factor of 24 for reverse bias and 2.6 for forward bias when the temperature increases from 240 to 300 K. The different device characteristics in forward and reverse biases suggest that different excitation mechanisms are responsible for EL.

Room-Temperature Electroluminescence from Erbium-Doped Porous Silicon Composites for Infrared LED Applications

The nanostructured matrix of porous silicon makes the material an ideal host for erbium because its very large surface area allows easy infiltration of the ions into the matrix and it readily oxidizes obtaining large concentrations of oxygen necessary for erbium emission. Erbium is infiltrated in the pores (<EQ 10-19 cm-3) by cathodic electrochemical migration of the ions followed by high temperature annealing (950 - 1100 degree(s)C). Electrochemical doping of porous silicon by erbium is simpler and of lower cost when compared to conventional techniques like ion implantation, epitaxial growth, and chemical vapor deposition used to fabricate erbium-doped c-Si structures. We demonstrate stable room- temperature electroluminescence at 1.54 micrometers from erbium- doped porous silicon devices under both forward and reverse bias conditions.

Silicon Light Emitters: Preparation, Properties, Limitations, and Integration with Microelectronic Circuitry

Starting with Canham’s discovery in 1990 that porous silicon (PSi) can emit bright light in the visible range of the spectrum, there has been a strong interest in silicon light emitters. PSi and other light-emitting forms of silicon contain nanostructures or crystallites in the nanometer size range. Throughout most of the 1990’s, the intense visible luminescence from nanoscale silicon crystallites has been a source of numerous investigations and considerable debate. Today, most of the controversies have been put to rest. However, much less has been written about nanoscale Si light-emitting devices, in part because some of their characteristics are less than ideal and not well understood. This paper reviews the status of nanoscale silicon light emitters. It starts with a survey of the manufacturing methods used to produce nanoscale Si. Next, key physical, optical, electrical, and structural properties of nanoscale Si are examined. The fabrication of electroluminescent devices (LEDs) is then discussed. We focus on the stability, efficiency, speed, and spectral characteristics of nanoscale Si light emitters. Recent results obtained on microcavity PSi LEDs and 1.5μm LEDs produced by doping PSi with erbium are discussed. Finally, the integration of PSi LEDs with microelectronic circuitry is reported and the prospects for practical devices are briefly examined.

Integration of Multilayers in Er-Doped Porous Silicon Structures and Advances in 1.5 μm Optoelectronic Devices

Infrared photoluminescence (PL) and electroluminescence (EL) from erbium-doped porous silicon (PSi) structures are studied. The PL and EL from the Er-doped PSi structures and the absence of silicon band edge recombination, point defect, and dislocation luminescence bands suggest that the Er-complex centers are the most efficient recombination sites. PSi multilayers with very high reflectivity (R ≥ 90%) in the 1.5 gim range have been incorporated in the structures resulting in a PL enhancement of over 100%. Stable and intense EL is obtained from the Er-doped structures. The EL spectrum is similar to that of the PL, but shifted towards higher energy. The unexpected shift in emission opens up the possibility for erbium related luminescence to encompass a larger part of the optimal wavelength window for fiber optic communications.

Erbium Emission from Silicon Based Photonic Bandgap Materials

Control over the 1.5 µm emission from erbium is desirable for communication and computational technologies because the erbium emission falls in the window of maximum transmission for silica based fiber optics. Tunable, narrow, directional, and enhanced erbium emission from silicon based 1-D photonic bandgap structures will be demonstrated. The structures are prepared by anodic etching of crystalline silicon and consist of two highly reflecting Bragg reflectors sandwiching an active layer. The cavities are doped by electro-migrating the erbium ions into the porous silicon matrix, followed by high temperature oxidation. By controlling the oxidation temperature, porosity, and thickness of the structure, the position of the erbium emission is tuned to emit in regions where the normal erbium emission is very weak. The erbium emission from the cavity is narrowed to a full width at half maximum (FWHM) of 12 nm with a cavity quality factor Q of 130, highly directional with a 20 degree emission cone around the normal axis, and enhanced by more than one order of magnitude when compared to its lateral emission. Erbium photoluminescence (PL) from porous silicon 2-D photonic bandgap structures is also demonstrated.