Dynamics of Photogenerated Charge Carriers in III-V Bulk and Nanowire Semiconductors

Research output: ThesisDoctoral Thesis (compilation)

Abstract

As a solution to solving energy consumption and environment problems, photovoltaics has become one type of the promising devices to convert solar energy into electricity directly. In some special areas like in space, a kind of photovoltaics with lightweight and reliable properties is needed to supply power. Therefore, photovoltaics based on the group III-V semiconductor nanowires has been emerged and developed nowadays. However, a large surface-to-volume ratio in nanowires leads to high-density surface traps and therefore could degrade the performance of photovoltaics. In general, the properties of applications are dominated by the behaviours of charge carriers in semiconductors. Therefore, it is important to understand all processes which are related to charge carriers in semiconductors.
In this thesis, a series of surface passivation methods are applied to lower the density of trap states and consequently improve the lifetime of photogenerated charge carriers in group III-V bulk and nanowire materials. We show that the GaNAs and AlGaAs passivation layers help to lower the trap density at the GaAs surface. Similarly, we have investigated the AlyIn(1-y)P passivated GaxIn(1-x)P nanowires with a great potential for multi-junction photovoltaic applications. Concerning InP nanowires, we investigated why optimal HCl etching provides less surface defects. Although the density of surface defect in InP is lower than in GaAs, an insulating layer is still needed to isolate the active InP nanowires and the electrodes. In this respect, we demonstrated that an appropriate POx/Al2O3 capped layer works as a passivation and insulating layer.
By means of several steady-state and time-resolved spectroscopies, such as time-resolved photoluminescence, transient absorption, and time-resolved terahertz spectroscopy, prospective passivation layers or conditions are screened for GaAs bulk, GaAs NW, InP NW, and GaInP NW materials. On the fundamental side, we find that charge trapping by several types of trap states dominates the primary steps of charge carrier dynamics and results in predominantly non-radiative recombination of photogenerated charges. Some trapping channels can be saturated via high charge generation rate under irradiation of the semiconductors by high intensity short optical pulses. Meanwhile, the atomic composition in ternary semiconductors, like Ga in GaxIn1−xP NWs plays a crucial role in the unexpected formation of deep traps. With the increase of Ga fraction, the fast electron trapping, hole trapping, and non-radiative recombination become more efficient.
These spectrum studies in this thesis not only help us to select a potential passivation method for group III-V bulk and nanowires materials, but also reveal the carrier behaviour in these materials. Based on these understanding, several methods of characterization of the optoelectronic materials performance are derived.

Details

Authors
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry

Keywords

  • Time-resolved spectroscopy, Group III-V semiconductor, Nanowires, Carrier recombination, Trapping, Passivation
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
  • Arkady Yartsev, Supervisor
  • Wang, Ergang, Assistant supervisor, External person
Thesis sponsors
  • Lund University
Award date2020 Sep 10
Place of PublicationLund, Sweden
Edition1
Publisher
  • Media-Tryck, Lund University, Sweden
Print ISBNs978-91-7422-750-5
Electronic ISBNs978-91-7422-751-2
Publication statusPublished - 2020 Sep 10
Publication categoryResearch

Bibliographic note

Defence details Date: 2020-10-16 Time: 13:00 Place: Lecture Hall C, Kemicentrum, Naturvetarvägen 14, Lund Join via zoom: https://lu-se.zoom.us/j/64274359500 External reviewer(s) Name: Sum, Tze-Chien Title: Professor Affiliation: Femtosecond Dynamics Lab, School of Physical & Mathematical Sciences, Nanyang Technological University, Singapore ---

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Related research output

Xiaojun Su, Xulu Zeng, Hynek Němec, Xianshao Zou, Wei Zhang, Magnus T. Borgström & Arkady Yartsev, 2019, In : Nanoscale. 11, 40, p. 18550-18558 9 p.

Research output: Contribution to journalArticle

Wei Zhang, Xulu Zeng, Xiaojun Su, Xianshao Zou, Pierre Adrien Mante, Magnus T. Borgström & Arkady Yartsev, 2017 Jul 12, In : Nano Letters. 17, 7, p. 4248-4254 7 p.

Research output: Contribution to journalLetter

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