Gupta, Vinod Kumar; (1998) Growth on patterned substrates for optoelectronic device application. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In this thesis growth on patterned substrates has been studied for the lateral bandgap control of the quantum well (QW) structures, utilising indium migration from the side facets onto the adjoining (100) surfaces, leading to the possibility of integration of multi- functional optoelectronic devices. InGaAs/GaAs/AlGaAs single quantum well (SQW) lasers and InGaAs/InAlAs QW heterostructures were grown by molecular beam epitaxy (MBE) on (100) GaAs and InP substrates respectively, patterned to produce (100) mesa top surfaces with angled side facets. Chemical beam epitaxy (CBE) was used for the growth of InGaAs/InP heterostructures over InP substrates, patterned into undercut mesas with (100) top surfaces using chemically assisted ion beam etching (CAIBE). Indium migration behaviour was compared by growing two InGaAs/GaAs/AlGaAs SQW graded index separate confinement heterostructure (GRINSCH) lasers by MBE over patterned GaAs substrates. The first laser was grown using As2 throughout, whereas the active region of the second laser was grown using As4. It is observed that the use of As4 facilitates the migration process whilst the use of As2 completely stops it. However, the broad area devices of both lasers exhibit extremely low threshold current densities and very high external quantum efficiencies. Split contact devices were made by growing InGaAs/GaAs/AlGaAs SQW GRINSCH lasers by MBE over variable step width mesas patterned on GaAs substrates using a newly designed mask. Electrical measurements on partially pumped devices showed bistability or pulsation behaviour depending on the bias conditions on the unpumped section. Growth of InGaAs/InP heterostructures by CBE on undercut mesas showed facetting behaviour producing atomically flat (111)B planes. Complete triangular shape structures bounded by very smooth (111)B facets were produced on mesas as narrow as 2.0 μm. This shows the strong possibility of growing one dimensional (1D) quantum wire structures, produced completely in-situ as a direct result of the growth process.

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