Highly Strained (InAs) M /(GaAs) N Multiple Quantum Well Based Resonant Tunneling Diodes on GaAs (100) Substrates and Th
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HIGHLY STRAINED (InAs)M/(GaAs)N MULTIPLE QUANTUM WELL BASED RESONANT TUNNELING DIODES ON GaAs (100) SUBSTRATES AND THEIR APPLICATION IN OPTICAL SWITCHING R. M. Kapre, Kezhong Hu, Li Chen, S. Guha*, and A. Madhukar Photonic Materials and Devices Laboratory, University of Southern California, CA 90089-0241.
ABSTRACT We report the realization of (a) an optically bistable switch using a strained resonant tunneling diode (RTD) and (b) highly strained RTDs exhibiting simultaneously high peak current densities (Jp) and peak-to-valley current ratios (PVR) suitable for high-speed electronic switching. Both of these make use of RTDs with (InAs)M/(GaAs)N strained short period multiple quantum well regions with AlAs barriers in a triple-well, double barrier structure. For the former, high contrast ratio (20:1) and an on state reflectivity of 46.5 % has been obtained at room temperature in an optically bistable switch involving a strained InGaAs/GaAs (100) multiple quantum well based asymmetric Fabty-Perot reflection modulator, detector, and a strained RTD and a Si field effect transistor. For the latter, we have obtained a Jp of 125 kAIcm 2 with a PVR of 4.7 at room temperature. The bistable nature of the resonant tunneling diode (RTD) I-V characteristics makes it suitable for a variety of switching applications including as a control element for optical switches, electronic pulse generators, etc. Optical signal processing and computing require the development of optical switching elements. The requirement for these applications include a low switching energy, hard limiting i.e. well defined output logic levels, large on/off ratio, high fanout, and fast response. Various HI-V quantum well based devices have been demonstrated for these applications. The use of the exciton red shift in a quantum well under applied bias - the quantum confined stark effect (QCSE) - to realize the self-electro-optic effect device (SEED) introduced by Miller et al. [1] has given rise to several schemes for realizing optical bistability. These include using the SEED with various loads such as a resistor [1], a photodiode [2], and another SEED [3]. Devices utilizing the exciton blue shift arising from the Wannier-Stark localization in a short period superlattice (SPSL) under bias in a p-i(SPSL)-n structure integrated with Bragg mirrors of appropriate reflectivities as the p and n regions ( the asymmetric FabryPerot configuration, ASFP) have achieved a high (>100:1) modulation contrast [4]. Such an ASFP modulator was combined with a Si-photodiode to achieve a diode-SEED (D-SEED) with optical bistability contrast ratio as high as 130 : 1 [4]. The basic SEED concept and its variations exploit the negative differential resistance (NDR) region of the detector or the modulator and thus require a significant overlap in the applied bias regimes needed for the NDR and light modulation in the modulator to achieve positive feedback. This constraint can be relaxed using a scheme proposed by Sakaki et al. [5] that exploits the NDR of a resonant tunneling diode co
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