InP/InAsP Quantum Discs-in-Nanowire Array Photodetectors: Design, Fabrication and Optical Performance

Forskningsoutput: AvhandlingLicentiatavhandling


This thesis focuses on processing and electro-optical investigations of two- and three-terminal photodetectors based on large arrays of around three million n+-i-n+ InP nanowires with embedded InAsP quantum heterostructures for broadband detection. First, we investigated the optoelectronic behavior of two-terminal photodetectors under selective 980 nm excitation of the 20 axially embedded InAsP quantum discs in each of the nanowires. The photodetectors show a non-linear optical response, which we attribute to a novel photogating mechanism, resulting from electrostatic feedback from trapped interface charge between the nanowire and SiOx cap layer, similar to the gate action in a field-effect transistor. From detailed analyses of the complex charge carrier dynamics involving these traps in dark and under illumination was concluded that electrons are trapped in two interface acceptor states, located at 140 and 190 meV below the conduction band edge. The non-linear optical response was investigated at length by photocurrent measurements recorded over a wide power range. From these measurements were extracted responsivities of 250 A/W (gain 320) @ 20 nW and 0.20 A/W (gain 0.2) @ 20 mW with a detector bias of 3.5 V, in excellent agreement with the proposed two-trap model. Finally, a small signal optical AC analysis was made both experimentally and theoretically to investigate the influence of the interface traps on the detector bandwidth. While the traps limit the cut-off frequency to around 10 kHz, the maximum operating frequency of the detectors stretches into the MHz region.
In the second part we report on device processing and optoelectronic characterization of the first reported three-terminal phototransistors based on similar InP/InAsP nanowire heterostructures, now with a buried global gate-all-around contact around the i-segment of the nanowires comprising the quantum discs. Furthermore, the results from detailed modeling of this device are presented and discussed. In particular, we highlight a unique possibility to electrically tune the spectral content of the photocurrent and the high gain-bandwidth product. The transparent ITO gate-all-around contact facilitates a radial control of the carrier concentration by more than two orders of magnitude in the nanowires and quantum discs. The transfer characteristics reveal two different transport regimes. In the subthreshold region, the photodetector operates in a diffusion mode with a distinct onset at the bandgap of InP. At larger gate biases, the phototransistor switches to a drift mode with a strong contribution from the InAsP quantum discs. Besides the unexpected spectral tunability, the detector exhibits a state-of-the art non-linear responsivity reaching 100 A/W (638 nm/40 W) @ VGS=1.0V/VDS=0.5V, and a response time of the order of s, limited by the experimental setup, in excellent agreement with a comprehensive real-device model.
  • Pettersson, Håkan, handledare
  • Borgström, Magnus, Biträdande handledare
Tilldelningsdatum2022 okt. 20
StatusPublished - 2022

Ämnesklassifikation (UKÄ)

  • Nanoteknik


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