P. Barnes

THE DESIGN AND APPLICATION OF III-V MULTIQUANTUM WELL OPTICAL MODULATORS

The application of an electric field across a quantum well structure induces a shift in the exciton dominated absorption edge. This effect is exploited in a number of optoelectronic devices including electro-absorption modulators, electron-refraction modulators, and optoelectronic logic devices. We will discuss how such modulators may be designed to operate at low voltages, with large changes in transmission or reflection and at high speeds. The choice of well widths, barrier widths, the use of coupled wells, and the enhancement due to Fabry Perot structures will all be considered. Results will be included for GaAs-GaAlAs, GaInAs-InP, and GaAs on silicon structures. Applications of these devices in optical interconnection of electronic circuits, and optoelectronic logic will be reviewed.

GaAs multiple quantum well microresonator modulators grown on silicon substrates

We report new results on the modulation characteristics of GaAs/AlGaAs asymmetric Fabry-Perot modulators grown on silicon substrates. We discuss factors affecting device performance and evaluate these by growing p-i-n quantum well diodes, and multilayer reflector stacks on silicon. Using data from these test structures we have designed an asymmetric microresonator modulator and achieve, experimentally, a 40% reflection change with only 5 V and a contrast ratio of 7.4 dB, also with 5 V.

GaAs / AlGaAs pin MQW structures grown on patterned Si substrates

Abstract We report structural and optical studies of a pin MQW structure grown on a patterned Si substrate. We find that a high density of microcracks in the directions are formed on the plain area of the substrate but that these are almost totally absent on the patterned areas. Photoluminescence measurements show a shift of QW emission to higher energies as island size is reduced with little change in intensity. These results show that good quality MQW device structures with reduced strain and freedom from microcracks can be grown on patterned Si.

Optical emission from GaAs/AlGaAs p‐i‐n multiquantum well structures grown on patterned Si substrates

Photoluminescence and cathodoluminescence have been used to investigate the strain in GaAs/AlGaAs multiquantum well structures grown on a thick GaAs buffer layer on a patterned silicon substrate. By growing the epitaxial GaAs only on ‘‘islands’’ of Si the density of microcracks is reduced by nearly two orders of magnitude. Although the biaxial tension is reduced in the vicinity of a microcrack, the strain is almost eliminated at the island edges. Strain is still present in the center of the islands but reduces with decreasing island size offering the possibility of relatively strain and microcrack free, small area optical devices on silicon substrates.