Experimental studies of proton-implanted GaAs-AlGaAs multiple-quantum-well modulators for low-photocurrent applications

We describe the first attempts to control photocurrent, and thus power dissipation, in surface-normal multiple-quantum-well (MQW) modulators. We have made detailed experimental studies of proton-implanted p-i-n GaAs-Al/sub x/Ga/sub 1-x/As MQW modulators having barrier layers of x=0.3, 0.45, and 1.0. Structures were implanted to levels of 1/spl times/10/sup 12/ cm/sup -2/, 1/spl times/10/sup 13/ cm/sup -2/, and 1/spl times/10/sup 14/ cm/sup -2/. Photocurrent progressively decreased with increasing implant-dose and barrier mole fraction (x). Exciton linewidths showed a strong voltage and implant dose dependence, demonstrating a tradeoff between photocurrent and modulation performance. We obtained our best results with x=1.0 barriers. For example, 1/spl times/10/sup 13/ cm/sup -2/-implanted asymmetric Fabry-Perot modulators were realized in which the optical performance was similar to that of unimplanted devices. The photocurrent responsivity was, however, only 0.007 A/W at 12.5 V bias. We report measurements of carrier lifetime in these materials that show the reduction in photocurrent arises from a reduction in lifetime due to implant-induced damage. In addition, the reduced lifetime decreases the optically-excited quantum-well carrier population, leading to an increase in cw saturation intensity. Specifically, 1/spl times/10/sup 13/ cm/sup -2/-implanted devices with x=1.0 have a saturation intensity of roughly 45 kW/cm/sup 2/, while unimplanted devices have 3.5 kW/cm/sup 2/. Asymmetric self electro-optic effect devices (A-SEED's) are demonstrated, and power dissipation issues associated with the use of low-photocurrent modulators in integrated systems are discussed.<
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