Yaser M. Haddara

Dependence of InGaP nanowire morphology and structure on molecular beam epitaxy growth conditions.

InGaP nanowires (NWs) were grown by the Au-assisted method in a gas source molecular beam epitaxy system. The dependence of InGaP composition, morphology and stacking fault density was studied with respect to group III and V impingement rate and size of the Au particle. Compositional analysis showed that the NWs had an In-rich core and a Ga-rich shell structure. The In incorporation within the NW became limited as the Au seed particle size diminished or the group III and V flux decreased. The NWs had wurtzite (WZ) crystal structure with zinc blende (ZB) segments (stacking faults). The density of the stacking faults decreased as the group III flux decreased and the group V flux increased.

A kinetic model for the oxidation of silicon germanium alloys

We propose a complete model for the oxidation of silicon germanium. Our model includes the participation of both silicon and germanium atoms in the oxidation process and the replacement by silicon of germanium in mixed oxides. Our model is capable of predicting, as a function of time, the oxide thickness, the profile of the silicon in the underlying alloy, and the profile of germanium in the oxide. The parameters of the model vary with temperature, alloy composition, and oxidizing ambient. The model shows excellent agreement with published results, with model parameters following trends consistent with the physical phenomena hypothesized. The presence of germanium catalyzes both the silicon and the germanium oxidation rates, and all reaction rates increase with increasing temperature. The resulting effective oxidation rate is enhanced, with respect to the oxidation of pure silicon, at all germanium concentrations. Mixed oxides form only in the case of high germanium concentrations, but at high temperature...

A low-power CMOS class-E power amplifier for biotelemetry applications

Designing efficient, fully integrated transceivers that could operate from very low supply voltages and for biomedical implantable electronic systems is a major challenge. This paper presents a fully integrated, 2.4 GHz class-E power amplifier (PA), with a class-F driver stage. The circuit was fabricated in a standard 0.18 /spl mu/m CMOS technology. Measurement results show a maximum drain efficiency of 38 % and a maximum gain of 17 dB. When operating from a 1.2 V supply, the PA delivers an output power of 9 mW with a power-added efficiency (PAE) of 33 %. The supply voltage can go down to 0.6 V with an output power of 2 mW and a PAE of 25 %. The circuit also has a second output to test the effects of using an on-chip filter in low-power designs. This work demonstrates the feasibility of using class-E PAs for short-range, low-power applications.

A Fully Integrated CMOS Power Amplifier Using Superharmonic Injection-Locking for Short-Range Applications

This work demonstrates the feasibility of using a superharmonic injection-locked oscillator as a power amplifier for short-range, low-power applications. This paper presents two fully integrated, differential superharmonic injection-locked power amplifiers (ILPA) operating at 433 MHz and 2.4 GHz. The two circuits were fabricated in a standard 0.18 μ m CMOS technology. Measurement results of the 2.4 GHz ILPA show a maximum gain of 31 dB from only one stage that occupies a chip area of only 0.6 mm2 with all components fully integrated. The ILPA delivers an output power of 7.6 dBm from a 1.5 V supply voltage with a power added efficiency of 36%.

Modeling the suppression of boron diffusion in Si∕SiGe due to carbon incorporation

We used the process simulator FLOOPS-ISE to implement a consistent model describing the diffusion behaviors of boron and carbon in silicon and silicon germanium. In particular, our model successfully accounts for boron and carbon behaviors in a wide range of sample structures and experimental conditions over the complete temperature range of 750–1070°C in inert and oxidizing ambients, and in the presence of implant damage. The structures studied include cases where the boron and carbon profiles are separated as well as cases where profiles overlap, cases with carbon in silicon and in SiGe, and our own recent experiments where boron diffusion within a SiGeC region has been characterized. We model carbon diffusion by the kickout and Frank-Turnbull mechanisms, and interstitial capture by substitutional carbon, and demonstrate that a model must incorporate all three effects to satisfactorily explain published data. We also include standard models for boron-interstitial clusters and {311} defects.

Modeling germanium diffusion in Si1−xGex/Si superlattice structures

We present a model for the interdiffusion of silicon (Si) and germanium (Ge) in silicon germanium/silicon (Si1−xGex/Si) superlattice (SL) structures. Both a vacancy exchange mechanism and an interstitial diffusion mechanism are considered in the proposed model. The effects of Ge on the diffusion properties of the SL are also considered and the conservation of lattice site constraints is accounted for. Output from the model is compared to experimental Ge interdiffusion profiles for samples annealed in the temperature range 770–1125 °C in inert ambient and in some cases in oxidizing ambient, where the experimental samples contained Ge fractions up to 30%. For anneal temperatures up to 1075 °C a vacancy exchange mechanism is sufficient to describe the interdiffusion mechanism in Si1−xGex/Si SL structures. For higher anneal temperatures interstitial diffusion mechanism dominates the interdiffusion process.

Impact of growth conditions on vacancy-type defects in silicon–germanium structures grown by molecular-beam epitaxy

Silicon–germanium layers of either 200nm or 250nm have been grown via molecular-beam epitaxy (MBE) on p-type (001) silicon substrates. Each sample was prepared using a unique combination of buffer-layer type, buffer-layer growth temperature, and layer Ge content. Vacancy-type defects have been identified using beam-based positron annihilation. These results, combined with those from previous work, indicate the size and concentration of defects in MBE grown SiGe layers depend strongly upon the buffer-layer growth temperature (T). For T>500°C vacancy point defect concentrations are below the detectable limit of the measurement. As T is decreased to 300°C, vacancy clusters form in the buffer layer and point defects appear in the SiGe film, even for a SiGe growth temperature of 500°C.

Integration of Heterogeneous Materials for Wearable Sensors

Wearable sensors are of interest for several application areas, most importantly for their potential to allow for the design of personal continuous health monitoring systems. For wearable sensors, flexibility is required and imperceptibility is desired. Wearable sensors must be robust to strain, motion, and environmental exposure. A number of different strategies have been utilized to achieve flexibility, imperceptibility, and robustness. All of these approaches require the integration of materials having a range of chemical, mechanical, and thermal properties. We have given a concise review of the range of materials that must be incorporated in wearable sensors regardless of the strategies adopted to achieve wearability. We first describe recent advances in the range of wearable sensing materials and their processing requirements and then discuss the potential routes to the integration of these heterogeneous materials.

A mathematical model for void evolution in silicon by helium implantation and subsequent annealing process

We propose a physically based model that describes the diameter and the density of voids in silicon introduced via high dose helium ion implantation and subsequent annealing. The model takes into account interactions between vacancies, interstitials, small vacancy clusters, and voids. Void evolution in silicon occurs mainly by a migration and coalescence process. Various factors such as implantation energy and dose, anneal temperature, atmospheric pressure, and impurity level in silicon can influence the migration and coalescence mechanism and thus play a role in the void evolution process. Values for model parameters are consistent with known values for point defect parameters and assumed diffusion limited reaction rates. A single “fitting parameter” represents the rate of cavity migration and coalescence and is, therefore, related to surface diffusion of adatoms. Results obtained from simulations based upon the model were compared to our experimental results and to previously reported experimental resul...

A 0.65V CMOS power amplifier for biotelemetry applications

In order to reduce the power consumption in biomedical implantable electronic systems, there is a major demand on reducing the supply voltage. This paper presents a fully integrated, 650 MHz class-E power amplifier (PA), with a class-F driver stage that is suitable for low-voltage operation. The circuit was fabricated in a standard 0.18 mum CMOS technology. Measurement results show a maximum drain efficiency of 15% and a maximum gain of 11.5 dB. When operated from a 0.65 V supply, the PA delivers an output power of 750 muW with a maximum power-added efficiency (PAE) of 10%. The circuit also has a second output to test the effects of using an on-chip filter in low-power designs. This work demonstrates the feasibility of using class-E PAs for short-range, low-power applications