Objectives of the Company

To develop a computational environment for modeling and simulating the behavior of nanoscale semiconductor heterostructures:

With increasing device density on conventional electronic chips, it becomes necessary to account for the cross-talk and the effects of quantum mechanical confinement of carriers. This means that the selection of semiconducting materials and the physical geometry of the layout of the heterostructures, at submicron levels, play a role in the electronic properties of the particular electronic component. Such a situation requires new computational and simulation tools which will model and predict the electronic response of a nanometer-scale device.

At QSA, we have been developing such a modeling environment within the framework of a finite element approach to the quantum mechanical computations. The types of structures that are being modeled at present include quantum wells (QWs), superlattices (SLs), and the resonant tunneling devices (RTDs) - all of these are layered structures grown today by molecular beam epitaxy. QSA collaborates in research with the Naval Research Laboratory, University of Houston, MIT, MIT Lincoln Laboratory, NEC Research Corporation, Purdue University, University of Missouri, Notre Dame University, and others, to authenticate and benchmark its computer codes. The applications at this level involve characterizing quantum structures grown for opto-electronic applications, development of new sources of coherent radiation (lasers), and in exploring new electronic mechanisms and physical effects associated with these layered structures. QSA has pioneered the computational methods; our collaborators within the US and our clients abroad have published over 300 publications in respected journals, such as the Physical Review, Applied Physics Letters, IEEE Journal of Quantum Electronics, Photonics Technology Letters, etc.

Versions of the software developed at QSA have been used at the NRL and the University of Houston to design new lasers in the 3-5 µm region of the near infrared spectrum for chemical sensing and for military applications such as missile detection and counter-measures. This is very encouraging since the new structures have been designed using the paradigm of Wavefunction Engineering which has come into its own because of the work done at QSA and the tools developed at QSA. The very first samples grown to specifications suggested by the software lased as predicted. These quantum cascade lasers involve an inter-band mechanism for the carrier transport through them and are designed using Type-II heterostructures.

More recently at QSA we have developed software for the design of inter-subband quantum cascade lasers operating in the mid-IR region of the spectrum as well as in the teraHertz (THz) region of the spectrum. We are working with MIT Lincoln Laboratory to design new structures that will lase at 4.5 microns, and with University of Massachusetts at Lowell for THz lasers. One of the most exciting modeling challenges is to develop simulation tools for the two- and three-dimensional confinement of carriers in quantum well wires (QWW) and quantum dots (Qdots). We have made substantial progress in the 2D modeling and are rapidly developing finite element codes for the quantum mechanical calculations required for predicting the optical and electronic properties of quantum dots.

We received Phase I Small Business Innovative Research (SBIR) grants from the Defense Advanced Research Projects Agency and from the Ballistic Missile Defense Organization (now known as Missile Defence Organization). Our Phase I work demonstrated feasibility of modeling and computational methods and algorithms for QWWs and Qdots. We are excited about the prospects for continued government and possible industry support for our algorithm development.

Our general approach and a description of tasks:

• At QSA, we have been developing sparse matrix solvers for complex valued matrices. The reason for the sparse matrix package is to allow very complex structures to be analysed on small memory systems.( For example, in quantum wire calculations we employ matrix sizes on the order of ~25,000x25000 having matrix occupancy with band-widths of ~200 along the diagonals.) This together with C++ programming for memory management allows the software to explore the most complex structures grown so far, including the Interband Quantum Cascade Lasers. We will be continuing the development of this matrix package.

• The software has three parts to it: for modeling layered structures, for QWWs and for Qdots. We have to include a number of physical features to the software so that it is useable by the research and development community in the near future and by the manufacturing industry as these novel devices come on-line. Given progress over the past few years in materials preparation and control over the design of heterostructures, we can anticipate the latter applications to becomes important within the next 5 years. This gives QSA the lead-time to develop a high quality, robust software for commercial applications in the opto-electronics industry.

• We are developing the codes with portability in mind, with the targetted systems being PC-based NT and the LINUX and UNIX operating systems. We currently support the LINUX, DEC-Alpha, and the SUN-Ultrasparc platforms. The porting to the NT is in progress.

• Parallelization within the shared memory scheme on dual-Pentium PCs will be implemented in the very near future.

  

  It should be clear that we have a long-term commitment to the business plan. We anticipate growth in our customer base with time. We can anticipate that this software will be in increasing demand in view of the demonstrated outcomes in terms of design of lasers and in the modeling and simulation of novel lasing mechanisms. The rapidly increasing overall need for quantum devices to achieve the next generation levels of computing at petaflops per second is also in our favor.

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