Gardner, Neil Robin; (1998) Electrical characteristics of silicon-doped GaAs lateral p-n junctions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes a systematic study of silicon dopant incorporation on various GaAs surfaces and the characterisation of lateral p-n junction structures formed by single-step growth on patterned substrates. Silicon is amphoteric in GaAs, doping the material n- or p-type dependant on the surface configuration and growth conditions. Lateral p-n junctions were therefore formed between suitable combinations of surfaces, grown under the correct conditions. Molecular Beam Epitaxy was the chosen growth method and the devices were fabricated on patterned (100) and (110) GaAs substrates. Studies of silicon doping behaviour on the (100), (110) and (N11)A (N=1,3,4) GaAs surfaces have shown that the conductivity type depends on growth conditions, and carrier saturation at high doping levels has been observed. Our results concur with published data and a Si incorporation picture is presented in terms of chemical bond energy considerations and the ratio between vacancy types on the growth surface. Lateral junctions were formed at the upper and lower boundaries between n-type (100) flat surfaces and p-type (311)A facets and p-type (110) flat surfaces and n- type (100) facets. Ga adatom migration between facets, as witnessed by the generation of new surfaces at the sidewall-flat boundaries has implications for dopant incorporation and defect generation in the junction regions. Electrical measurements revealed two main current mechanisms, dominant over different sections of the voltage characteristic. Under low bias, a tunnel current was observed and this was ascribed to indirect electron tunnelling into band-tail states, followed by recombination via phonon emission. Recombination and diffusion current were dominant under high bias conditions. The value of the calculated ideality factor was found to be dependant on the relative magnitudes of the majority carrier densities on each side of the depletion region. Electrical results are discussed in terms of dopant incorporation and compensation.

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