Guo, Daqian; (2021) III-V Quantum Structured Infrared Photodetectors Directly Grown on Silicon. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Direct growth of III-V infrared photodetectors on silicon substrates is a promising so- lution for realising low-cost and large-format infrared focal plane arrays. However, this heteroepitaxial growth technique will generate various defects due to the dissimilarities between III-V materials and Si. These defects can severely damage the performance of a detector. In this thesis, different III-V quantum structured infrared photodetectors directly grown on Si are investigated to understand how different structures react to the defects. The experimental chapters begin with reporting an InGaAs/GaAs quantum dot infrared pho- todetector (QDIP) on Si. By utilising a Si substrate with a high degree of offcut along with dislocation filter layers, antiphase domains have been eliminated and the threading dislocation density has been reduced by ∼4 orders of magnitude. The QDIP shows a dual-band photoresponse at 80 K. To reduce the noise, a sub-monolayer QD quantum cascade photodetector on Si was designed. This structure has led to a distinct reduction of dark current and noise, achieving a high operating temperature of 160 K. To further boost the quantum efficiency of infrared photodetectors on Si, InAs/GaSb type-II superlattice (T2SL) photodetectors were also studied in this thesis. Generally, T2SL photodiode structures are more sensitive to material defects than QDs. Moreover, the surface leakage current contributes to a high level of dark current. InAs/GaSb T2SL photodiodes and barrier detectors have been grown on GaAs and Si substrates. Transmission electron microscopy and X-ray diffraction results confirm that the strain energy has been released at the heteroepitaxy interface and the threading dislocation density has been reduced by ∼3 orders of magnitude. The bulk dark current has been reduced by implementing an nBp barrier design. As a result, a T2SL nBp detector on GaAs with surface passivation has been shown to be capable of operating at 190 K without external bias. The work described in this thesis shows that there is great potential to improve the detector performance by using novel detector designs. Future work should focus on structure optimisation, as well as material quality im- provements, in order to achieve both low dark current and high quantum efficiency. High- operating temperature detectors on Si can be attempted to further explore the potential of III-V quantum structured infrared photodetectors. Specific recommendations are made for candidate structures. In order to be compatible with the mainstream Si micro-electronics industry, fabrication on (001) Si substrates will be required. Research towards this objec- tive is therefore also proposed.

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