Research Projects:

             The primary focus of Molecular and Nanoelectronics (M&N) group at Karachi Institute of Economics and Technology (KIET) currently is the physical and empirical device modeling of compound semiconductor based high speed Heterojunction Bipolar Transistors (HBTs). System design is an iterative process as illustrated in Figure 3, research projects that are currently being pursued at KIET cover many areas of this entire design cycle as detailed below.

Physical Device Modeling of HBTs:

            Physical modelling is based on the underlying physics of the device and gives due consideration to device processing as well. It is suitable for device designing because it encompasses physical insight by virtue of which physical models are predictive. Even in case of miniaturisation, as long as, it does not drastically change the underlying physical mechanism, these models can be easily adapted.

Figure 3—Complete Design Cycle for MMIC ICs [1]

This project encompasses the development of physical models for InP based Double Heterojunction Bipolar (DHBT). SILVACO ATLAS [4] was previously used to develop these models; currently MINIMOS-NT[5] TCAD tool is being explored to further enhance these models. The wafers are Molecular Beam Epitaxy (MBE) grown and the DC and RF measurements of the devices are carried out by Microelectronics and Nanostructures (M&N) research group at The University of Manchester (UoM), UK. KIET has signed an agreement of research collaboration with UoM.

Figure 4—(A) Device structure and (B) meshing of InAlAs/InGaAs DHBT model [1]

Institute of Microelectronics, University of Austria, Vienna played a pivotal role in the development of the MINIMOS-NT modelling tool. They have agreed to provide technical help and may even be able to host researchers/students from KIET.


            Students desirous of pursuing this research should have interest in semiconductor electronics with good understanding of any circuit simulatior like PSPICE. They will be required to take relevant graduate level courses for example “Advanced fundamentals of semiconductors” and “High speed semiconductor devices” to bring them up to speed with the research activities of the group. Students should be available especially during summer to proceed abroad to conduct research at our collaborating institutions.  

1.1.2  Empirical Device Modeling

The purpose of device modelling is to represent phenomena occurring within the device and to be able to reliably predict the behaviour of an anticipated device; however for circuit level simulation where the number of devices is in large number, it is more important to analytically represent the device output behaviour with minimum mathematical complexity.
Figure 5—Large-signal Agilent HBT model [6]

This leads to the necessity of empirical models which mainly target to fit the measured data with the help of model parameters. There have been several advancements in the empirical device models of HBTs beyond the basic Gummel-Poon model; for example UCSD [7] (University of California, San Diego) model is one of the most comprehensive device model covering many of the HBTs’ distinct features like velocity modulation, Kirk effect etc. UCSD model was further improved especially in its mathematical robustness by Agilent HBT [8] and FBH model [9].
Figure 6—Measured RF data and Agilent HBT model of InAlAS/InGaAs DHBT [1]
This project encompasses the development of large-signal empirical model for InP based DHBT to be used in the design and simulation of high speed, low power digital circuits based on Emitter Coupled Logic (ECL) gates. These circuits have wide range of applications as depicted in Figure 2. These devices are fabricated at the University of Manchester, UK and its on-wafer DC and RF measurements are also carried out there; however, the empirical device modelling and circuit design and simulations will be carried out locally. Another international collaboration with the Royal Melbourne Institute of Technology (RMIT), Australia has been signed to facilitate the RF measurements of these devices up to a frequency of 40 GHz.


            The graduate students desirous of pursuing this research should have interest in semiconductor electronics and have good knowledge of PSPICE or similar software. In case of deficient background knowledge they should immediately sign up for the graduate courses “Advanced fundamentals of semiconductors” and “High speed semiconductor devices”. Students should be available especially during summer to proceed abroad to conduct research at our collaborating institutions.

1.2 Research Collaborations

         1.2.1    M&N group, The University of Manchester, UK.

         1.2.2    School of Electrical and Computer Engineering, Royal Melbourne   Institute of Technology (RMIT), Australia.

         1.2.3    Institute of Microelectronics, University of Vienna, Austria.


[1]        M. Mohiuddin, "InGaAs/InAlAs DHBT for high-speed, low-power digital applications," in Faculty of Engineering and Physical Sciences, vol. PhD. Manhcester: The University of Manchester, 2010, pp. 259.

[2]        M. Rodwell, E. Lobisser, M. Wistey, V. Jain, A. Baraskar, E. Lind, J. Koo, Z. Griffith, J. Hacker, M. Urteaga, D. Mensa, R. Pierson, and B. Brar, "THz Bipolar Transistor Circuits: Technical Feasibility, Technology Development, Integrated Circuit Results," 2008 Ieee Csic Symposium, pp. 1-3, 2008.

[3]        J. D. Cressler, "Emerging Application Opportunities for SiGe Technology," presented at IEEE Custom Integrated Circuits Conference, San Jose, CA, 2008.

[4]        ATLAS manual: SILVACO International, 4701 Patrick Henry Drive, Bldg. 1, Santa Clara, USA, 2005.

[5]        "MINIMOS-NT," in Device and Circuit Simulator: Institute of Microelectronics, University of Vienna, Austria, 2004.

[6]        M. Iwamoto and D. Root, "AgilentHBT: A Large-Signal Model for GaAs and InP HBTs," 2003.

[7]        "HBT Model Equations. rev9.001a 3/2000.." San Deigo:, 2000

[8]        "Agilent HBT Model," in Nonlinear Devices Manual: Agilent Technologies, 2006.

[9]        M. Rudolph, Introduction to Modeling HBTs. Norwood: Artech House, Inc., 2006.