Role Of Nonradiative Recombination Research Articles

Elucidating the role of non-radiative processes in charge transfer of core–shell Si–SiO2 nanoparticles

Crystalline silicon is the most commonly used material in photovoltaics but has limitations due to its high cost and non-tunable band gap. A new approach of using inexpensive, non-toxic materials with layers that have different band gaps which absorb a wide range of the solar spectrum has the potential to dramatically increase the efficiencies and lower the costs. Core–shell Si–SiO2 nanoparticles are ideally suited for the photovoltaic application and have been synthesised by different groups in an array of sizes allowing for absorption in a wide spectral range. A theoretical investigation of fundamental charge transfer processes in these systems can potentially lead to improved devices. Calculations on a model core–shell interface with the formula Si264O160 which features a silicon layer sandwiched between two SiO2 layers were performed using the Vienna ab initio software package. The Perdew–Burke–Ernzerhof functional in the basis of plane waves was used along with pseudopotentials to simulate electronic structure. The nuclear motion was considered using ab initio molecular dynamics. The density of states, absorption spectrum, partial charge densities, and radiative recombination lifetimes have been calculated. This interface shows quantum confinement behaviour similar to a particle in a box. The role of non-radiative recombination was also determined by relaxation dynamics.

Degradation of InGaN lasers: Role of non-radiative recombination and injection efficiency

With this paper we propose a detailed study of the gradual degradation of InGaN-based laser diodes and Light-Emitting Diodes submitted to electro-thermal stress. The two device structures have been processed from the same epitaxial wafer. Our purpose is to compare the behavior of the two devices by means of electro-optical measurements, electroluminescence characterization, and near field emission measurements. We demonstrate that: (i) stress induces a decrease in the optical power and an increase in threshold current; (ii) the two failure modes are strictly linked each other, and correlated to the increase in defect-related current components, indicating a substantial increase in defect density during degradation; (iii) analysis of characteristic temperature and near-field emission measurements do not indicate any strong variation of injection efficiency nor current confinement of the devices.

Role of nonradiative recombination in the degradation of InGaAsP/InP-based bulk lasers

The role of nonradiative recombination in the degradation of InGaAsP/InP buried-heterostructure bulk lasers with semi-insulating current-blocking has been investigated by current-voltage (I-V), output power response (I-P), and differential carrier lifetime measurements. Changes in the I-P characteristic show nonradiative recombination to be main cause of degradation; internal losses having negligible influence. This was confirmed by carrier lifetime measurements, which showed the increase in the nonradiative recombination rate to be proportional to the increase in the threshold current. Other recombination processes remained unaffected. A degradation-generated increase in forward bias current below threshold was, for the first time, interpreted in terms of an equivalent circuit. Results show the rate of nonradiative recombination to increase and be proportional to results from the more laborious carrier lifetime method. Observed changes in the reverse bias characteristic are, for the first time, shown to be caused by field-assisted thermal emission from weakly interacting donor-acceptor pairs created during degradation. Pair separation is 8-10 nm. One bandgap level lies 0.36 eV from one edge and the other close to the other edge. A decrease in the series resistance showed out-diffusion of interstitial Zn donors from the p-InP:Zn cladding layer to take place. Pairs are created by interaction of Zn interstitials with defects in the active layer.