AlxGa1-xAs/AlyGa1-yAs multiple quantum well structures for visible wavelength optical modulator a

摘要

Abstract: There is increasing interest in visible wavelength optical modulators compatible with storage media such as LiNbO$-3$/ and organic polymer materials. Multiple quantum well (MQW) structures with AlGaAs QWs allow the fabrication of optical devices operating at much shorter wavelengths than conventional GaAs QW devices which operate in the vicinity of 860 nm. We show bias-dependent photocurrent (PC) measurement results from p-i-n MQW samples containing 10 nm Al$-x$/Ga$-1$MIN@x$/As QWs with x-values ranging from 0 to 0.54 and corresponding wavelengths ranging from 860 to 570 nm. The barriers in each sample are 5 nm thick and have 30% more Al than the wells. The measured PC is proportional to the photon flux absorbed in the sample and, therefore, can be used to determine the quality of the material for absorption modulation. PC characteristics comparable to those of a GaAs/Al$- 0.30$/Ga$-0.70$/As MQW sample are obtained for wavelengths as short as 640 nm (QW x- value as high as 0.38). These spectra have sharp exciton features that maintain their general peak shape and steeply falling lower energy edge under applied reverse bias. Shorter wavelength samples, 610 nm (x equals 0.46) and 570 nm (x equals 0.54), do not show good modulation characteristics, but may potentially be improved by further optimizing the structure design and growth conditions. With the same MQW structures and growth conditions used to produce the above samples, optical modulators operating at wavelengths as short as 640 nm can be fabricated. !14