Optoelectronic Device Applications of Self-Organized In(Ga,Al)As/Ga(Al)As Quantum Dots
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0. QASAIMEH *, W. D. ZHOU *, J. SINGH *, P. J. MCCANN ** and K. NAMJOU
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* Solid State Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109-2122, [email protected] ** School of Electrical and Computer Engineering, Laboratory for Electronic Properties of Materials, University of Oklahoma, Norman, OK 73019-1023
ABSTRACT Self-organized growth of strained semiconductor heterostructures has enabled the realization of ordered arrays of quantum dots that can be incorporated into the active region of electronic and optoelectronic devices. Highly uniform In(Ga)As/Ga(Al)As with greatly reduced photoluminescence linewidths (FWHM=19 meV, T=17K) have been grown and characterized. Various aspects of carrier dynamics in these dots, such as measurement of carrier relaxation times and the modulation bandwidths of quantum dot lasers, estimation of the tunneling time in vertically coupled dots along with tuning of the intersubband electronic energy levels have also been studied. The favorable relaxation times can be exploited to realize far infrared emission and detection based on intersubband transitions in the dots. The optoelectronic properties of the dots and the dynamics of carriers therein are also extremely attractive for high-speed wavelength switching and the design of electro-optic modulators. The electro-optic coefficients in the quantum dots have been measured and the linear E-O coefficient, r, =2.6 x10-1 m/V, is found to be comparable to that in LiNbO3. I. INTRODUCTION The understanding of strained layer epitaxy and, in particular, self-organized epitaxy has fueled research and development in the characterization of the islands that are formed and in their application as quantum dots in the active regions of microelectronic and optoelectronic devices"' 3'. Although the phenomenon of island growth under strain is applicable to a variety of heterostructures systems, in the context of this paper the discussion will be centered on the growth of In(Ga)As on Ga(Al)As. It is now generally accepted that the dots, or boxes, are near pyramidal in shape (Figure 1) with a height and lateral extent of 6-8 nm and 20-22 nm, respectively. The strain within the dots and their bandstructure and electronic states have been calculated using a 8-band k.p formulation for both conduction and valence bands 5 and the optical properties related to the transition between the electron and hole bound states have also been elucidated 6 . The calculations have been complemented by a rich variety of experiments to understand the electronic and optical properties of the dots 7',' 9 and the dynamics of hot carriers therein10 11 ' . Fig. 1: (a) High resolution TEM image of a single self organized quantum dot grown by deposition of 16 periods of 0.25 ML InAs/0.25 ML GaAs, separated by 5s pauses. 195 Mat. Res. Soc. Symp. Proc. Vol. 618 0 2000 Materials Research Society
Concurrent with materials growth and characterization, great strides have been made in the application of thes
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