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

MS, University of Cincinnati, 2003, Engineering : Electrical Engineering

Device modeling using a two dimensional, drift-diffusion approach utilizing a commercial numerical device simulator has been used to investigate the operation and performance of InP/GaAsSb heterojunction bipolar transistors (HBTs). GaAsSb lattice matched to InP has an energy bandgap (0.72 eV) that is similar to that of InGaAs (0.75eV) so that Sb-based HBTs have been proposed as a replacement for InGaAs-based HBTs. In particular, the conduction band lineup is more favorable at the base-collector,which makes the GaAsSb-based HBTs especially attractive for double heterojunction bipolar transistors (DHBTs) where higher breakdown voltages are desired. In this work,the results of device modeling will be compared initially with recent experimental reports to validate the modeling approach. Then the design and operation of the devices will be examined to investigate the factors controlling device performance in order to facilitate improvements in device design. The degradation of device performance at high currents due to the formation of a parasitic barrier in the collector region and the base push out effects is examined. Finally, a device structure with improved high frequency performance is described.

Committee: Dr. Kenneth P. Roenker (Advisor) Subjects:

MS, University of Cincinnati, 2005, Engineering : Electrical Engineering

The advent of the optical fiber amplifier has extended the distance between two repeaters and changed the role of the photodetector in an optical receiver in an optical fiber communication system. This new development enables amplification of the signal in its optical form before detection so that the photodetector must now be capable of responding to the high frequency, high power input optical signal without distortion, thereby eliminating the post detection amplification in electrical domain. The conventional p-i-n photodetector, which uses a depleted intrinsic layer as the light absorbing layer suffers from space charge buildup at high input optical power due to the slower movement of the photogenerated holes and so cannot respond adequately. A new type of photodetector, the Uni-Traveling Carrier Photodiode (UTC-PD), overcomes the limitations of the PIN by using a heavily doped p-type photoabsorption layer and a fully depleted, intrinsic wide bandgap collection layer. In the UTC-PD, photogenerated holes are the majority carrier in the absorption layer so their speed of response is determined by the dielectric relaxation time, which is normally very small (~ picoseconds). Therefore, only electrons are active carriers in an UTC-PD and as they move faster than the holes, the device response is much faster. In this thesis study, we have simulated the performance of a novel GaAsSb/InP UTC-PD as a possible replacement for the previously demonstrated InP/InGaAs UTC-PD. The study was performed using a commercial numerical device simulator ATLAS from Silvaco International for a 1.55 µm wavelength. This novel UTC-PD utilizes a p+ GaAsSb with a bandgap energy of 0.72 eV as the absorption layer and a Gaussian doping profile, n- InP as the depleted collection layer, n+ InP as the n+ contact, p+ InAlAs as the main electron blocking layer, p+ InGaAs as the p+ contact and a thin layer of p+ InGaAlAs as a spacer layer between GaAsSb absorption layer and InAlAs electron blocking (open full item for complete abstract)

Committee: Dr. Kenneth Roenker (Advisor) Subjects: