Three subjects related to epitaxial GaAs-GaAlAs optoelectronicdevices are discussed in this thesis. They are:
1. Embedded Epitaxy
This is a technique of selective multilayer growth of GaAs-Ga1-xAlxAs single crystal structures through stripe openings in maskinglayers on GaAs substrates. This technique results in prismatic layersof GaAs and Ga1-xAlxAs "embedded" in each other and leads to controllableuniform structures terminated by crystal faces. The dependence of thegrowth habit on the orientation of the stripe openings has been studied.Room temperature embedded double heterostructure lasers have beenfabricated using this technique. Threshold current densities as lowas 1.5 KA/cm2 have been achieved.
2. Barrier Controlled PNPN Laser Diode
It is found that the I-V characteristics of a PNPN device can becontrolled by using potential barriers in the base regions. Based onthis principle, GaAs-GaAlAs heterostructure PNPN laser diodes have beenfabricated. GaAlAs potential barriers in the bases control not onlythe electrical but also the optical properties of the device. PNPN laserswith low threshold currents and high breakover voltage have been achieved.Numerical calculations of this barrier controlled structure are presentedin the ranges where the total current is below the holding point andnear the lasing threshold.
3. Injection Lasers on Semi-Insulating Substrates
GaAs-GaAlAs heterostructure lasers fabricated on semi-insulatingsubstrates have been studied. Two different laser structures achievedare: (1) Crowding effect lasers, (2) Lateral injection lasers. Experimentalresults and the working principles underlying the operation ofthese lasers are presented. The gain induced guiding mechanism is usedto explain the lasers' far field radiation patterns. It is found thatZn diffusion in Ga1-xAlxAs depends on the Al content x, and that GaAscan be used as the diffusion mask for Zn diffusion in Ga1-xAlxAs.Lasers having very low threshold currents and operating in a stablesingle mode have been achieved. Because these lasers are fabricated onsemi-insulating substrates, it is possible to integrate them withother electronic devices on the same substrate. An integrated device,which consists of a crowding effect laser and a Gunn oscillator ona common semi-insulating GaAs substrate, has been achieved.
