Yasser M. El-Batawy

Polarization dependence of absorption by bound electrons in self-assembled quantum dots

In this paper, the effects of the incident light polarization on the bound to continuum linear absorption coefficient of quantum dot devices have been investigated. The study is based on the effective mass theory and the Non Equilibrium Greens Function formalism. For the bound to continuum component of the absorption coefficient, both of in-plane and perpendicular polarization effects are studied for different sizes of conical quantum dots. Generally, decreasing the dots dimensions results in an increase of the in-plane polarized light absorption and in moving the absorption peak towards longer wavelengths. On the other hand, decreasing the dots dimensions results in a decrease of the perpendicularly polarized light absorption coefficient and in moving the absorption peak towards longer wavelengths.

Modeling light absorption by bound electrons in self-assembled quantum dots

A theoretical model of the absorption coefficient of quantum dot devices is presented. Both of bound to bound absorption and bound to continuum absorption are taken into consideration in this model which is based on the effective mass theory and the nonequilibrium Greens function formalism. The results of the model have been compared with a published experimental work and a good agreement is obtained. The effects of the dot dimensions and electron filling on the bound to continuum absorption coefficient are also investigated. In general, increasing the dot filling increases the absorption and decreasing the dots dimensions will increase the absorption and move the absorption peak towards longer wavelengths.

Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors

A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.

Modeling of mushroom waveguide photodetector

Waveguide photodetectors (WGPDs) are promising candidates for applications in high-speed optical communications and interconnections. In these high-speed photodetectors, both high bandwidth and high external quantum efficiency can be achieved simultaneously. Mushroom-WGPD is proposed to overcome the trade-off between the capacitance and contact resistance of the photodetector. In this article, a physical model of the mushroom-WGPD is presented including both time and frequency responses of this photodetector and how they depend on the parameters of the photodetector. A SPICE model for mushroom-WGPD including all the parasitics is also presented, showing the dependence of the transfer function of this model on the dimensions and the material parameters of the photodetector. The effects of the parasitics are also studied for different photodetector areas. The characteristics of mushroom-WGPD are studied for two cases, first without an inductor added in series with the load resistance and second, if an induc...

Biasing effects on the characteristics and the optimization of mushroom waveguide photodetectors (WGPDs)

Waveguide photodetectors (WGPDs) are considered a leading candidate to overcome the bandwidth-quantum efficiency trade-off as the flow of the photon and carrier fluxes are perpendicular to each other enabling high date rate applications. Mushroom-WGPD was proposed to overcome the trade-off between the capacitance of the photodetector and the contact resistance. In this paper, an extended calibrated circuit model for mushroom-WGPD, including the effect of the biasing of the photodetector, is presented so resulting in the feasibility of a complete circuit simulation of the entire photoreceiver circuit. The effects of the biasing over the performance of Mushroom-WGPDs have been explored for different loads and different dimensions of the device. Based on the studies of different parameters for design and materials, optimization has been performed for the mushroom-WGPD. With this optimization, the optimal values of the thickness of the absorption layer to produce the highest bandwidth of the photodetector are obtained for different biasing values. These optimizations are performed for different areas of the photodetector and also for different load resistors, and they result in a significant improvement in the performance of the mushroom-WGPDs.

Resonant cavity enhanced photodetectors: Theory, design and modeling

Abstract Photodetector is one of key component in optoelectronic integrated circuits (OEICs). Photodetectors are extensively used in optical communication systems, optical interconnections, and biomedical imaging, and they typically operate from visible to near-infrared wavelength. For most applications, one or more of the following performance characteristics including high-sensitivity or quantum efficiency, high-speed, low noise, high dynamic range may be required. However, in optimizing the design of photodetectors, there is a key performance trade-off between quantum efficiency or sensitivity, and speed. To overcome this trade-off and simultaneously obtain high speed and high sensitivity, resonant cavity enhanced photodetectors (RCE-PDs) are used. Here, we discuss, in detail, various RCE-PD structures with an emphasis on theory, design, modeling and performance characteristics. Important research results are summarized and ideas on how to improve the design of RCE-PDs are presented. The time and frequency response, important for high-speed or high bit rate applications, are discussed from the perspective of detectors in real applications. For optimized design of OEICs, circuit models are indispensable. Therefore, we discuss circuit models for RCE-PDs, including the effects of parasitic elements on time response characteristics as well as device design optimization. The various materials combinations that have been used for RCE-PDs as well as different types of photodetectors are summarized. Finally, the rapidly emerging, high-performance RCE quantum dot photodetectors for mid-infrared applications are introduced.

Effect of self assembled quantum dots on carrier mobility, with application to modeling the dark current in quantum dot infrared photodetectors

A theoretical method for calculating the electron mobility in quantum dot infrared photodetectors is developed. The mobility calculation is based on a time-dependent, finite-difference solution of the Boltzmann transport equation in a bulk semiconductor material with randomly positioned conical quantum dots. The quantum dots act as scatterers of current carriers (conduction-band electrons in our case), resulting in limiting their mobility. In fact, carrier scattering by quantum dots is typically the dominant factor in determining the mobility in the active region of the quantum dot device. The calculated values of the mobility are used in a recently developed generalized drift-diffusion model for the dark current of the device [Ameen et al., J. Appl. Phys. 115, 063703 (2014)] in order to fix the overall current scale. The results of the model are verified by comparing the predicted dark current characteristics to those experimentally measured and reported for actual InAs/GaAs quantum dot infrared photodet...

Gear nano antenna for plasmonie photovoltaic

In this paper a novel nanoparticle structure has been presented to be used in plasmonic photovoltaic to enhance its efficiency. The proposed structure is a silver gear structure that is expected to make good enhancement of light absorption inside the semiconductor forming the photovoltaics (PV) in the visible range of frequencies (200-800 THz). The nano antenna particle is embedded inside the photovoltaics and produces highly confined near-field around the nanoparticle and withing the semiconductor. The extinction cross-section of the proposed nanoparticle in vacuum has been calculated versus the wavelength. Also, the modes of fields are studied and finally the effect of embedding this gear nanoparticle in a silicon photovoltaic is investigated by comparing its absorption with the conventional disk nanoparticle. The proposed structure enhances the light absorption in the near infrared region, which improves the efficiency of the PV solar cells.

Biasing dependent circuit modeling and optimization of resonant cavity enhanced PIN photodetectors (RCE-PIN-PDs)

Resonant Cavity Enhanced Photodetectors (RCE-PDs) are a possible solution to overcome the trade-off between bandwidth and quantum efficiency in the conventional photodetectors. In RCE-PDs, thin absorption layer gives rise to a large bandwidth, while the multiple passes of light in the absorption layer due to the resonant cavity increases the quantum efficiency. In this paper, an extended calibrated circuit model for RCE-PIN-PD is presented. This model includes the effects of the biasing of the photodetector resulting in the feasibility of a complete circuit simulation of the entire photoreceiver circuit. The effects of the biasing over the performance of RCE-PIN-PDs have been studied for different loads and different thicknesses of the absorption layer of the photodetector. Based on the studies of different parameters for design and materials, optimization has been performed for the RCE-PINPDs. With this optimization, the optimal values of the thickness of the absorption layer to produce the highest bandwidth of the photodetector are obtained for different biasing values. These optimizations are performed for different areas of the photodetector and also for different load resistors, and they result in a significant improvement in the performance of this type of photodetector.