Sohail Zafar - Academia.edu (original) (raw)

Papers by Sohail Zafar

The purpose of this study was to determine if selected personal characteristics, facets of job sa... more The purpose of this study was to determine if selected personal characteristics, facets of job satisfaction, and the two dimensions of organizational justice (distributive justice & procedural justice) significantly explained variance in the organizational commitment of Pakistani university teachers. In addition, the present study examined the influence of organizational commitment on two organizational outcomes-job performance and turnover intentions. Data were gathered from 125 full-time teachers from 33 universities in the three major cities of Pakistan: Lahore, Islamabad/Rawalpindi, and Peshawar. The results of the study indicate that the personal characteristics, facets of job satisfaction and two dimensions of organizational justice as a group were significantly related to organizational commitment of teachers. Individually, distributive justice and trust in management were found to be the strongest correlates of commitment. Moreover, commitment was found to be negatively related to turnover intentions (-.40) and positively related to a self-report measure of job performance (.32).

Journal of Vacuum Science & Technology A, 1995

ABSTRACT The tunneling current through tin (∼50 Å) silicon dioxide films is observed to have a sm... more ABSTRACT The tunneling current through tin (∼50 Å) silicon dioxide films is observed to have a small oscillatory component at high electric fields. Three main results involving the oscillatory component of the tunneling current are reported. First, a new and improved analysis for obtaining the oscillatory component from the current measurements is described. Then, using this analysis, the dependence of the oscillatory component on oxide thickness and SiO 2 /Si interface roughness is studied. The thickness study shows that the oscillation amplitude decreases exponentially as the distance traveled by the electron in the conduction band of SiO 2 increases. This decrease is attributed to the scattering effects and the mean free path of the electron in SiO 2 is estimated to be 6 Å, in agreement with previous reports. The roughness study is performed on thermally oxidized purposely roughened Si surfaces, and the roughness is characterized by the atomic force microscopy. The oscillations in the tunneling currents show no dependence on the interface roughness, indicating that the roughness at the Si surface has little effect on the thickness uniformity of thermally grown thin oxide films and that oxide films grow uniformly over the roughened Si surfaces for at least the first 50 Å or so. © 1995 American Vacuum Society

We have developed a manufacturing friendly process for CIS solar cells that includes all-solid-st... more We have developed a manufacturing friendly process for CIS solar cells that includes all-solid-state processing and an inert gas, atmospheric pressure selenization/anneal. Present efficiencies are in the 9-10% range with Vocs at 400+ mV. Correlations between processing and performance have been established. Vocs have been advanced to 430 mV using an etching process. These results combined with insights provided by a recombination model indicate that Voc s in excess of 500 mV are within reach

In spite of the highly successful development of CIGS at the laboratory level, successful commerc... more In spite of the highly successful development of CIGS at the laboratory level, successful commercialization of the technology has not yet been demonstrated. This is largely due to limited understanding and control of the growth mechanisms. We have developed extensive understanding of these mechanisms for all solid state processing of CIGS(This is a 2-step process which we designate as 2SSS) and are currently using this understanding to guide the development of a CIGS pilot line with square foot area capability. In this paper we focus on the selenization mechanisms which are critical to overall performance and manufacturability. While for manufacturing purposes we employ the 2SSS process, we also use co-deposition to assist understanding. For all processes we find an interrelationship between Se and Ga incorporation. This impacts both materials utilization and film performance. With our novel 2SSS process we can exercise better control over the underlying mechanisms and better optimize the materials utilization/performance tradeoff. This also enables the use of deposition pathways that result in better performance and yield at the manufacturing level that might not be utilized because of excessive Se and/or Ga waste.

Journal of Vacuum Science & Technology A, 1995

ABSTRACT We have deposited ZnO:Al films with state‐of‐the‐art electro‐optical properties by react... more ABSTRACT We have deposited ZnO:Al films with state‐of‐the‐art electro‐optical properties by reactive magnetron sputtering from a zinc target. Films with resistivities of 5×10-4 Ω cm, good optical properties over the visible and near infrared, and with good uniformity are routinely produced. Resistivities down to 1.7×10-4 Ω cm have been achieved but are accompanied by expected losses in optical properties. The fundamental mechanisms driving performance are largely determined by an interplay between microstructure and ionized impurity scattering. At the deposition level the parameters which control these mechanisms are substrate bombardment and substrate temperature. At substrate temperatures of 350 °C and sufficient source‐to‐substrate distances doping efficiencies approaching 100% can be achieved. At carrier concentrations of 4×1020 cm3 or higher there is a crossover from defect controlled transport to ionized impurity scattering dominated transport which constrains improvements in conductivity. This combined with free carrier effects on optical properties sets the limits for the electro‐optical properties of these films. This understanding can be used to further develop the deployment of these films as transparent conductors. © 1995 American Vacuum Society

We have developed techniques for effectively incorporating Ga in CIGS within the confines of our ... more We have developed techniques for effectively incorporating Ga in CIGS within the confines of our manufacturing-friendly process. Near Cu/(In+Ga)=1 collection lengths of 1-2 μm can be attained resulting in consistent Jsc's of 40 mA/cm2. As the metal ratio is decreased below 1, there is an unusual abrupt increase in Eg of 50 mV and a significant deterioration of electronic properties. These properties are discussed in terms of interplay between process control of kinetics and thermodynamics and the dictates of the phase diagram. A key objective which we have attained is the ability to independently optimize surface and bulk properties. Using these techniques we have raised our Voc's above 500 mV for devices with band gaps of 0.95 eV and have achieved 13% device efficiency

Highly uniform films of reactively sputtered ZnO:Al with resistivity of 5×10-4 Ω-cm and good opti... more Highly uniform films of reactively sputtered ZnO:Al with resistivity of 5×10-4 Ω-cm and good optical properties have been produced. The resistivity can be reduced to 1-2×10-4 Ω-cm with some loss in near-IR transmission. Al incorporation drops rapidly with increasing Tss , while carrier concentration (n) increases resulting in increases in doping efficiency of up to ×30. Transport properties are controlled by bombardment induced damage and ionized impurity scattering. The later results in a correlation between mobility and n which combined with the effect of free carriers on optical properties leads to fundamentals-driven design tradeoffs for solar cell use

IEEE Transactions on Circuits and Systems for Video Technology, 1992

Abstract-A video compression scheme based on the wavelet representation and multiresolution motio... more Abstract-A video compression scheme based on the wavelet representation and multiresolution motion compensation (MRMC) is presented in this paper. The multiresolution/ multifrequency nature of the discrete wavelet transform is an ideal tool for representing images and video ...

IEEE Journal on Selected Areas in Communications, 1993

A multiscale video representation using wavelet decomposition and variable block-size multiresolu... more A multiscale video representation using wavelet decomposition and variable block-size multiresolution motion estimation (MRME) is presented in this paper. The multiresolutiodmultifrequency nature of the discrete wavelet transform lends itself as an ideal tool for representing video sources with different resolutions and scan formats including video telephone, NTSC/PAL/SECAM, and upcoming HDTV standards. The proposed variable block-size MRME scheme utilizes the motion correlation among different scaled subbands and adapts to their importance at different layers. This algorithm is well suited for interframe HDTV coding applications and facilitates the conversion and interactions between different video coding standards. Four scenarios of the proposed motion-compensated coding schemes are implemented and compared with 1-pixel, 1/2-pixel, and 1/4pixel accuracies based on entropy, energy distribution, computational complexity, and associated overheads on the displaced residual subbands. A pel-recursive motion estimation scheme is also implemented in a multiresolution form. It is believed that the scalable architecture and adaptive processing of different video formats make the proposed scheme suitable for the broadcast environment where various standards may coexist simultaneously.

A video compression scheme based on the wavelet representation and multi-resolution motion estima... more A video compression scheme based on the wavelet representation and multi-resolution motion estimation (MRME) is presented in this paper. The multiresolution/multifrequency nature of the discrete wavelet transform lends itself as an ideal tool for representing images and video signals. Wavelet transform decomposes a video frame into a set of sub-frames with different resolutions corresponding to different frequency bands. These multiresolution frames also provide a representation of the global motion structure of the video signals at different scales. The motion activities for a particular sub-frame in different resolutions are hence highly correlated since they actually specify the same motion structure at different scales. In the MRMC described the Section 4, motion vectors in higher resolution are predicted by the motion vectors in the lower resolution, and are refined at each step. In particular, we propose a variable block-size MRMC scheme in which the size of a block is adapted to its level in the pyramid. This scheme not only considerably reduces the searching and matching time but also provides a meaningful characterization of the intrinsic motion structure. The variable-size MRMC approach also avoids the drawback of the constant-size MRMC in describing small object motion activities. After wavelet decomposition, each scaled wavelet tends to have different statistical properties. An adaptive truncation process similar to [CHEN 84] was implemented and a bit allocation scheme similar to that in the transform coding is examined by adapting to the local variance distribution in each scaled wavelet. Based on the wavelet representation, variable-size MRMC approach and a uniform quantization scheme, four variations of the proposed motion-compensated wavelet video compression system are presented in Section 6. It is shown that the motion-compensated wavelet transform coding approach out-performs the conventional transform coding scheme in terms of the signal-to- noise ratio as well as the subjective performance.

IEEE Transactions on Broadcasting, 1991

A new predictive block-matching mo�ion estimation scheme is proposed in this paper for efficIent ... more A new predictive block-matching mo�ion estimation scheme is proposed in this paper for efficIent video codec design. The proposed scheme is based on the "inertia" effect of natural TY video scenes and takes advantage of the motion vectors obtained in the previous frames. Not only motion searching time and overhead are significantly reduced, the propo . sed , scheme also provides realistic motion tendency, whIch IS very useful for frame skipping/interpolation techniques. These advantages are also demonstrated by some experimental results obtained on Abekas video system.

European Neuropsychopharmacology, 1991

... Sohail Zafar Ya-Qin Zhang* John S. Baras I ... Another search algorithm for the direction of ... more ... Sohail Zafar Ya-Qin Zhang* John S. Baras I ... Another search algorithm for the direction of the motion vectors is based on conjugate direction presented by Srinivasan and Rao [7]. Starting at the center of the block the vertical direction is kept fixed while the horizontal direction is ...

IEEE Transactions on Broadcasting, 1991

IEEE Transactions on Circuits and Systems for Video Technology, 1993

The statistical characteristics of full-motion video sources using motion-adaptive variable-bit-r... more The statistical characteristics of full-motion video sources using motion-adaptive variable-bit-rate coding techniques is studied. Analytical models are developed to describe the behavior of the coded video signals based on the encoder structure. The video-compression algorithm used is in compliance with the general MPEG syntax and bit-stream definition. Statistical characteristics associated with each block type and their aggregate are presented. A composite model to represent the number of bits per field for the encoded video traffic that comprises multiple autoregressive models for the number of blocks per field and the number of bits in each coded block is derived. The statistics measured from a sample video sequence are compared to those obtained by the model and it is observed that the model captures the coded video behavior for each block type and their combination reasonably well. This model can be used to further study the cell-generation process of full-motion video codecs and the aggregation of such video sources at the statistical multiplexers

European Neuropsychopharmacology, 1991

A novel motion estimation/compensation scheme for full-motion interframe video compression is pro... more A novel motion estimation/compensation scheme for full-motion interframe video compression is proposed. This scheme is based on prediction of interblock motion information by using minimum absolute difference block matching and hence substantially increases the searching and computation efficiency. A comparison is made with the `optimal' full motion searching scheme for a standard test sequence. The experimental results show that the proposed scheme provides a computationally efficient algorithm in a real-time video communication environment

IEEE Transactions on Broadcasting, 1991

One of the methods of measuring and calculating quality factor Q in the laboratory is the spectra... more One of the methods of measuring and calculating quality factor Q in the laboratory is the spectral ratio technique. The method utilizes the spectral amplitudes recorded by propagating a waveform through the sample and again through a nonattenuating reference sample with the same dimensions as the sample. This technique assumes that Q is constant over the experimental frequency band and thus it is independent of frequency. A new technique that utilizes discretization of the spectral ratio yielded variable differentials of the logarithmic of the discretized spectral ratio interval. This differential is directly related to the wave attenuation from source to receiver, at the discretized frequency. The technique was used to show that Q decreases with increasing frequency. The statistical average of Q was found to be equal to the frequency independent Q derived by the traditional spectral ratio technique while the variance of the Q provided error estimate in the form of confidence intervals.

Journal of Vacuum Science & Technology A, 1995

IEEE Transactions on Circuits and Systems for Video Technology, 1992

IEEE Journal on Selected Areas in Communications, 1993

IEEE Transactions on Broadcasting, 1991

European Neuropsychopharmacology, 1991

IEEE Transactions on Broadcasting, 1991

IEEE Transactions on Circuits and Systems for Video Technology, 1993

European Neuropsychopharmacology, 1991

IEEE Transactions on Broadcasting, 1991