Tu Hoang

Strong Efficiency Improvement of SOI-LEDs Through Carrier Confinement

Contemporary silicon light-emitting diodes in silicon-on-insulator (SOI) technology suffer from poor efficiency compared to their bulk-silicon counterparts. In this letter, we present a new device structure where the carrier injection takes place through silicon slabs of only a few nanometer thick. Its external quantum efficiency of 1.4middot10-4 at room temperature, with a spectrum peaking at 1130 nm, is almost two orders higher than reported thus far on SOI. The structure diminishes the dominant role of nonradiative recombination at the n+ and p+ contacts, by confining the injected carriers in an SOI peninsula. With this approach, a compact infrared light source can be fabricated using standard semiconductor processing steps

Influence of Dislocation Loops on the Near-Infrared Light Emission From Silicon Diodes

The infrared light emission of forward-biased silicon diodes is studied. Through ion implantation and anneal, dislocation loops were created near the diode junction. These loops suppress the light emission at the band-to-band peak around 1.1 mum. The so-called D1 line at 1.5 mum is strongly enhanced by these dislocation loops. We report a full study of photoluminescence and electroluminescence of these diodes. The results lead to new insights for the manufacturing approach of practical infrared light sources in integrated circuits.

Dimensional scaling effects on transport properties of ultrathin body p-i-n diodes

Device scaling has been a subject of research for both optoelectronics and electronics. In order to investigate the electronic properties of scaled devices we studied lateral p-i-n structures using thin silicon on insulator (SOI) or poly-Si layers of varying dimension. With the help of these structures we try to explain the size dependencies on electronic transport properties. Further, we also propose a new device concept called charge plasma diode.

The effect of dislocation loops on the light emission of silicon LEDs

Recently, different and apparently contradicting results were published regarding the influence of crystal defects on the light emission efficiency of silicon LEDs at room temperature (Wai Lek Ng). In this paper we report our results on light emission of silicon p/sup +/n diodes with various defect engineering approaches. The p/sup +/ region was formed either by ion implantation or by diffusion; and optionally, additional lattice damage was created by silicon ion implantation. The experiments clearly indicate that lattice defects have a detrimental effect on light emission, contrary to the results published in recent years.

Valence Band Offset Measurements on Thin Silicon-on-Insulator MOSFETs

The effect of quantum confinement in thin silicon-on-insulator double-gate MOSFETs has been directly determined from subthreshold current measurements for the first time. By comparing temperature-dependent subthreshold characteristics of p-type devices with different silicon layer thicknesses, the offset in the valence band edge induced by spatial carrier confinement in these very thin silicon layers was measured electrically. Changes in the band structure are important for future CMOS devices such as FinFETs.

Engineering of Dislocation-Loops for Light Emission from Silicon Diodes

Luminescence properties of silicon light emitting diodes with engineered dislocation loops were investigated. Dislocation loops were formed by Si+-ion implantation above and below metallurgical p+-n junction followed by an annealing step. The diodes showed characteristic dislocation (D-band) and band-to-band luminescence. Measurements of carrier-injection level dependence of the D-band signal intensity were performed. The results are in agreement with the model for dislocation luminescence, which suggests rediative transition between two, dislocation-related shallow levels. A gradual blue-shift of the D-band peak positions was observed with an increase in the carrier injection level in electroluminescence and photoluminescence. A supposition about existence of strong Stark effect for the excitonic dislocation states allows explaining the observations. Namely, in the build-in electric field of the p-n junction the exciton energies are red-shifted. The injected charge carriers lower the field and thus cause the blue-shift of the peak positions. A fitting of the data using the quadratic Stark effect equation suggests 795 meV for the spectral position of D1 peak at 300 K and 0.0186 meV/(kV/cm)2 for the characteristic constant.

SOI-LEDs with Carrier Confinement

Silicon-On-Insulator (SOI) technology exhibits significant performance advantages over conventional bulk silicon technology in both electronics and optoelectronics. In this chapter we present an overview of recent applications on light emission from SOI materials. Particularly, in our work we used SOI technology to fabricate light emitting diodes (LEDs), which emit around 1130 nm wavelength with an external quantum efficiency of 1.4 × 10−4 at room temperature (corresponding to an internal quantum efficiency close to 1 %). This is almost two orders of magnitude higher than reported earlier for SOI LEDs. This large improvement is due to three carrier confinement mechanisms: geometrical effects, quantum-size effects, and electric field effects. Our lateral p+/p/n+ structure is powered through two very thin silicon slabs adjacent to the p+/p and n+/p junction. Such use of thin silicon films aims to reduce the p+ and n+ contact area and to confine the injected carriers in the central lowly doped p-region. With this approach, we realized an efficient compact infrared light source with high potential switching speed for on-chip integration applications.

Influence of Interface Recombination in Light Emission from Lateral Si-Based Light Emitting Devices

The influence of interface recombination on the electroluminescence profile of a lateral p+/p/n+ light emitting diode fabricated on Silicon On Insulator (SOI) materials has been experimentally investigated. Our device resembles a MOSFET fabricated on SOI (1), except that the source region has opposite doping to the drain. By controlling the voltage bias at the poly gate on top of active emitting region in association with a bias on the silicon substrate under the active region we were able to diminish the non-radiative recombination component at Si/SiO2 interface and therefore enhance the radiative recombination in the thin film SOI. When the diode is working under constant current condition, we observe an increased light output of ~ 20 % as the gate and/or the substrate are biased negatively. The intensity profile across the device is also strongly influenced. To understand the device thoroughly, the structure has also been simulated showing agreement with experimental results.