A densely and monolithically integrated photonic chip on indium phosphide is greatly in need for data transmission but the present day’s level of integration in InP is very low. Silicon enjoys a unique position among all the semiconductors in its level of integration. But it suffers from its slow signal transmission between the circuit boards and between the chips as it uses conventional electronic wire connections. This being the bottle-neck that hinders enhanced transmission speed, optical-interconnects in silicon have been the dream for several years. Suffering from its inherent deficient optical properties, silicon is not supposed to offer this feasibility in the near future. Hence, integration of direct bandgap materials, such as indium phosphide on silicon, is one of the viable alternatives. This thesis addresses these two issues, namely monolithic integration on indium phosphide and monolithic integration of indium phosphide on silicon. To this end, we use two techniques, namely selective epitaxy and heteroepitaxy by employing hydride vapor phase epitaxy method. The first part deals with the exploitation of selective epitaxy for fabricating a discrete and an integrated chip based on InP. The former is a multi-quantum well buried heterostructure laser emitting at 1.55 µm that makes use of AlGaInAs and InGaAsP as the barrier and well, respectively. We demonstrate that even though it contains Al in the active region, semi-insulating InP:Fe can be regrown. The lasers demonstrate threshold as low as 115A/cm2/quantum well, an external quantum efficiency of 45% and a characteristic temperature of 78 K, all at 20 oC. Concerning the integrated device, we demonstrate complex and densely packed buried arrayed waveguide (AWG) structures found in advanced systems-on-the-chip for optical code-division multiple-access (O-CDMA). We present a case of an error-free 10 Gb/s encoding and decoding operation from an eight-channel AWGs with 180 GHz channel spacing. Selective epitaxial growth aspects specific to these complicated structures are also described and guidance on design implementation of these AWGs is given. Mass transport studies on these AWGs are also presented. The second part deals with various studies on and relevant to epitaxial lateral overgrowth (ELOG) of high quality InP on silicon. (i) ELOG often encounters cases where most part of the surface is covered by mask. From the modeling on large mask area effects, their impact on the transport and kinetic properties has been established. (ii) It is known that ELOG causes strain in the materials. From synchrotron X-ray measurements, strain is shown to have large effect on the mask edges and the underlying substrate. (iii) The combination of strain and the influence of image forces when reducing the opening dimensions in ELOG has been modeled. It is found to be very beneficial to reduce openings down to ~100 nm where effective filtering of dislocations is predicted to take place even in vicinity of the openings. We call it nano-ELOG. (iv) By combining the modeling results of nano-ELOG and of a pre-study of ELOG on pure InP, a novel net pattern design is invented and experimented for nano-ELOG of InP on Si. PL measurements together with transmission electron microscopy observations indicate beneficial effects of small size openings (200 nm) compared to 1000 nm openings. (v) ELOG of InP on silicon-on-insulators together with a multi-quantum well structure grown on it has been demonstrated for the first time. This is particularly interesting for integrating silicon/silicon dioxide waveguides with InP. / QC 20100902

The continuing refinement of crystal growth techniques has made possible the fabrication of semiconductor superlattices where the period can be as small as one lattice constant. Prediction of many of the properties of such systems requires a detailed description of their electronic structure. In this thesis, a self-consistent pseudopotential method which includes a parametrization scheme has been used to calculate the electronic properties of (GaAs)n(AlAs)n superlattices with n ranging from 1 to 4. The parametrization scheme is used to reproduce energy gaps at the principal symmetry points for the bulk constituents and the resulting parameter set is employed in all subsequent calculations. The n=l superlattice is found to be indirect with the conduction band minimum at R (equivalent to the zincblende L point) and all the thicker systems are pseudodirect in good agreement with experimental results. The lowest conduction band state at the zone centre for all systems is found to be mainly X-derived reflecting the importance of zone translating effects here. By analysing the states near to the band edges, the observed pattern of confinement in states of the n=l superlattice shows the band offsets to have at most a small role, in contrast to the thicker systems where a definite relationship was established. Moreover, the results suggest that Dingle's "15% rule" is consistently violated and that a valence band offset of about 30-40% is obtained which changes little with layer thickness. Attempts to study the effects of hydrostatic pressure on the n=3 superlattice were in part successful and predicted quite complex behaviour for the electronic states. Much of the discrepancy between the results obtained and the experimental data was attributed to the inadequacies of the empty-core pseudopotential to model the ions.

Optical and electron beam lithography has been used to fabricate high mobility GaAs:AlGaAs heterojunction FETs in which the current is controlled by Schottky barrier gates with novel geometries. The two dimensional electron gas (2DEG) at the heterojunction interface had a low temperature mobility of ~250,000 cm<SUP>2V<SUP>-1s<SUP>-1</SUP> and a carrier concentration of 4.3x10<SUP>11cm<SUP>-2</SUP>. Narrow channels of the 2DEG were defined by means of a split gate which consisted of two gold pads 15μm long, separated by ~1μm. A negative voltage applied to the gate removes carriers from beneath the gate resulting in a narrow channel in the gap. The channel width can be reduced to zero by further decreasing the gate voltage. At low temperatures (T ≤ 4.2K) the electron phase coherence length, Lφ, is greater than the width, W, and the transport is quasi one dimensional. Analysis of the low temperature magnetoconductance showed that for a channel of width ~450AA the phase coherence length varied as Lφsim 0.16μ m(T/K)^-0.35±0.06. A similar result was obtained from an analysis of the universal conductance fluctuations in channels of width ~ 1800AA. This suggests that the dominant electron scattering mechanism was due to electromagnetic fluctuations in the 2DEG for which Lφ would be expected to vary as T^-1/3. For high magnetic fields (O < B ≤ 8T) the magnetoconductance showed oscillations which were explained in terms of the magnetic depopulation of one dimensional subbands. A number of fine gate FETs were made with gate lengths of ~ 1000AA. The I-V characteristics of a strongly depleted channel were measured at 4.2K and it was found that I ∝V<SUP>3/2</SUP> so that the current flow was dominated by space charge effects. For larger source drain biases I ∝ V and this was explained as being due to velocity saturation. The second voltage differential δ2V/δI<SUP>2</SUP> showed structure at ~ 40meV and ~ 80meV and this was attributed to optic phonon emission by hot electrons.

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