Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

Contactless, nondestructive measurements of minority carrier lifetime by transient microwave reflectance (TMR) and photoluminescence are used to study the carrier dynamics of several ternary materials: InGaAs, GaAsSb, and InAsSb. As contactless measurements, TMR and photoluminescence can determine quality of as-grown wafers. The minority carrier lifetime is inversely proportional to the diffusion component of the dark current and can be used as an indicator of device performance, without the need for full device fabrication. The ability to yield useful information about wafer quality without the time and cost used for fabrication allows for quick feedback to growers. GaAsSb and InGaAs lattice-matched to InP are candidates for short-wave infrared (SWIR) detection at 1.5 μm, a wavelength used for eye safety and optical communication. The high speed or low signal applications at this wavelength benefit from the use of separate absorber, charge, and multiplier (SACM) avalanche photodiodes (APDs). In these devices, the absorber is optimized for detection at the wavelength of interest, and the multiplier is optimized for gain through impact ionization. InGaAs-based SACM APDs are a mature technology and are available commercially. The multipliers paired with InGaAs, however, typically have high noise. Research into low-noise multipliers has resulted in the demonstration of AlGaAsSb as a low noise material. When AlGaAsSb is paired with InGaAs, the grading material AlInGaAs creates a conduction band offset with AlGaAsSb, limiting bandwidth. GaAsSb lattice-matched to InP has similar properties to InGaAs and could be implemented without a conduction band offset due to the grading material being AlGaAsSb. When a GaAsSb/AlGaAsSb SACM APD was demonstrated, it was found to have higher dark current than commercial InGaAs-based devices. Because these materials are so similar, this was unexpected. As mentioned, the diffusion component of the dark current is inversely proportio (open full item for complete abstract)

Committee: Sanjay Krishna (Advisor); Steve Ringel (Committee Member); Preston Webster (Committee Member); Anant Agarwal (Committee Member); Shamsul Arafin (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2004, Electrical Engineering

The epitaxial integration of III-V semiconductors with Si is of interest for photovoltaics since Si substrates offer a lighter, stronger, and cost effective platform for device production. By using compositionally step-graded SiGe layers to 100% Ge, the 4% lattice-mismatch between Si and GaAs and In 0.49 Ga 0.51 P is accommodated; this method has produced record low threading dislocation densities (TDD) of 1x10 6 cm -2 in fully relaxed the Ge/SiGe/Si (SiGe) substrates. In this dissertation, this method of III-V/Si integration is used for the development of GaAs and In 0.49 Ga 0.51 P single junction (SJ) solar cells and In 0.49 Ga 0.51 P /GaAs dual junction (DJ) solar cells, integrated on a Si platform. As such, we report that the minority carrier electron lifetime in p-type GaAs grown on Si is lower than that of holes in n-type GaAs at a given TDD and is a consequence of the higher mobility of electrons. This lower lifetime produced higher reverse saturation currents and lower open-circuit voltages for n+/p compared to p+/n configuration GaAs cells grown on SiGe with the same TDD. The higher performance of the p+/n GaAs/Si cell, by virtue of its higher open-circuit voltage, has demonstrated a record terrestrial efficiency of 18.1% and has been produced in areas up to 4 cm 2 with no degradation in cell performance. In 0.49 Ga 0.51 P SJ cells were integrated on Si substrates and an increase in depletion region recombination component of the reverse saturation current with TDD was also measured. A p+/n polarity preference for In 0.49 Ga 0.51 P on Si was demonstrated, although, the lower mobility of both carriers in In 0.49 Ga 0.51 P compared to GaAs, suggests a greater TDD tolerance. Based on these SJ results, the first realization of an In 0.49 Ga 0.51 P/GaAs DJ cell on Si with an output voltage greater than 2 V was demonstrated. A comparison with an identical DJ cell on GaAs found that the DJ cell on Si retained 91% of open-circuit voltage and 99% of short-circuit cu (open full item for complete abstract)

Committee: Steven Ringel (Advisor) Subjects: Physics, Condensed Matter