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Investigation Of Plasmonics And Photochemical Machining Technology On GaP Surface

Posted on:2016-01-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:G J LinFull Text:PDF
GTID:1108330461485547Subject:Materials science
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The development of semiconductor materials and technologies has greatly changed our life. Ⅲ-Ⅴ compound semiconductor materials, which are represented by GaP, GaN and GaAs, have been applied extensively due to their unique band structures and high electron transfer mobilities. As the energy problem becomes more and more serious, Ⅲ-Ⅴ compound semiconductor materials have been paid great attentions for their applications on photovoltaic devices (solar cells) and solid state lighting (light emitting diodes, LEDs).Gallium phosphide (GaP), which has an indirect band gap of 2.26 eV, is a potential candidate for solar cells, LEDs and photodetectors in the visible region. In this dissertation, we developed the technology of interference laser assisted wet chemical etching and localized surfaces plasmon resonances (LSPRs) of metallic nanoparticles have been creatively applied on wet photochemical etching, surface patterning fabrication and photoluminescence (PL) of GaP, and achieved very significant results. There are five chapters in this dissertation. They are "Chapter 1-Introductions; Chapter 2-Surface plasmon enhanced photochemical etching of p-GaP and wavelength selectivity; Chapter 3-LSPRs of metallic nanostructures enhanced PL of GaP and surface-enhanced Raman scattering (SERS); Chapter 4-Maskless surface patterning of AlGaInP based LEDs by photochemical laser interference etching; Chapter 5-Conclusions and prospects", respectively. Detailed research contents are as follows:Chapter 1:In this chapter, we first made a detailed literature review for Ⅲ-Ⅴ compound semiconductor materials and surface plasmon resonances (SPRs) of metallic nanoparticles. The main contents include 1) characteristics and applications of Ⅲ-Ⅴ compound semiconductors,2) properties of GaP crystal and its applications in AlGaInP LEDs,3) etching technologies related to semiconductor materials and laser interference lithography,4) SPRs of metallic nanoparticles and their applications on photochemical reactions, PL, and SERS.Chapter 2:The Au nanoparticles have been used to increase the photochemical wet etching rate of p-GaP. We also investigated the effects of laser wavelength on photochemical wet etching of p-GaP. The effects of LSPRs have been analyzed in details.1) We used a variety of chemical etchants and found that only the mixture of HF and H2O2 can etch p-GaP under 532 nm laser irradiation.2) Mutually hinged Au nanostructures with a width of-50 nm were fabricated by a sputtering-annealing process. We realized photochemical etchings of blank and Au-coated p-Gap samples by using laser irradiation of different wavelengths.3) A significant enhancement of the photochemical etching of p-type GaP by Au plasmonic nanostructures was obtained when the sample was irradiated by a 532 nm laser. Note that the etching rate for the Au-coated samples is 10 times greater than the blank samples at the initial etching stage. Our analysis shows that photogenerated holes can be transferred from Au nanostructures to p-GaP sample under 532 nm laser irradiation. The number of holes reaching the defect (dislocation) states (Ed) for Au-coated samples is a few orders of magnitude greater than the blank.4) We also found that the rate enhancement of the photochemical etching process is wavelength selective. Only 532 nm laser can effectively increase the photochemical etching rate, while lasers of other wavelengths (e.g.,375 nm,405 nm,445 nm, and 473 nm) all leads to slightly reduced etching rates. The reason lies on the fact that only 532 nm laser can effectively excite LSPRs of Au nanostructures.5) In the course of photochemical etching of blank p-GaP samples, the fastest rate is obtained under 532 nm laser irradiation. We believe that the electrons can transit directly to the conduction band bottom of GaP (Xic) under 532 nm laser irradiation. As for other laser wavelength, the photogenerated electrons will transit to the Γ point (ΓIC) of the Brillouin zone of GaP, and the lifetime of electrons in the Γ point (ΓIC) is relatively short because of rapid recombination of electron-hole pairs. The slight increase of etching rate for 375 nm and 405 nm laser due to the reduced light penetration depth.Chapter 3:Au and Ag nanoparticles were fabricated by a sputtering-annealing process and galvanic displacement reactions, and the LSPRS of Au and Ag nanostructures enhanced photo luminescence of GaP and SERS have been investigated.1) Au and Ag nanoparticels are randomly distributed on GaP surface. The results show that the size and density of Au nanoparticles increase rapidly with the sputtering time, while for Ag nanoparticles, the sputtering time only affect the density of Ag nanoparticles, the size (-30 nm) does not change significantly with the sputtering time.2) We find that the light emission from GaP wafer is enhanced by metallic Au and Ag nanostructures. The results show that the maximum enhanced factor of Au nanostructures coated samples 5.6 appears at the sputtering time of 5 s corresponding to size and density of Au nanostructures being 15 nm and 2.48 ×1010 cm-2 respectively. While for Ag nanostructures coated samples, the maximum enhanced factor is 14.5, for sample with a same sputtering time of 5 s corresponding to size and density of Ag nanostructures is 30 nm and 1.12 ×1010 cm-2 cm-2 respectively. The reflectance spectra demonstrate that the scattering effect of metallic nanostructures can increases the light absorption. The time resolved photoluminescence (TRPL) results show that the radiative recombination rate can be accelerated by the LSPRs of Ag nanoparticles.3) Au nanostructures can be spontaneously grown by a galvanized process on GaP. In contrast, the growth of Ag nanostructures must be accompanied by UV irradiation.4) The Raman spectra of rhodamine 6G (R6G) show that the Raman enhancement effect of Au nanoparticles is much better than that of Ag nanoparticles. When the reaction time is 120 s, the Raman enhancement factor for Au nanoparticles is up to 105, while it is 104 for Ag nanoparticles.Chapter 4:In this chapter, we implement maskless surface patterning of GaP by photochemical laser interference etching, and two-dimensional (2D) quasiperiodic patterns on AlGaInP based red LEDs is fabricated by this method. We find that the light extraction efficiency of AlGaInP based red LEDs can be dramatically increased by the 2D quasiperiodic patterns.1) Design and set up a laser interference photochemical wet etching system. The 2D quasiperiodic patterns with a period of 150±10 nm is fabricated on p-GaP surface by laser interference photochemical wet etching, which is far less than half of the source wavelength.2) Polydimethylsiloxane (PDMS) grating is prepared through a strain mediated method. We have relized the 2D quasiperiodic patterns preparation by PDMS grating interference assisted wet etching.3) The 2D quasiperiodic patterns were fabricatied on p-GaP window layer of AlGaInP based red LEDs by laser interference assisted wet etching. The electrical performance tests show that the etching has negligible effects on the electrical properties of the LED chips. The optical performance tests show that the light extraction efficiency of LEDs have been improved by-70% than that of the original sample. Our results also show that the brightness of the samples fabcriated by interference laser etching is significantly higher than that of the samples etched by single beam laser, which is of great significance for the fabrication of high brightness LEDs.Innovations of this dissertation include:(1) the LSPRs of Au nanoparticles were applied to the photochemical etching of GaP with enhanced etching rate; (2) the wavelength selectivivity of the photochemical etching was demonstrated, with underlying principles discussed based on band bending and defect levels at the semiconductor/etchant interface; (3) the enhanced photoluminescence (PL) emission of GaP by LSPRs of Au and Ag nanoparticles was confirmed; (4) quasi-periodic patterns were fabricatd by photochemical laser interference etching on GaP based LEDs with enhanced light extraction efficiency.In conclusion, firstly, we apply the localized surfaces plasmon resonance of metallic nanoparticles to photochemical wet etching of p-GaP and find that LSPRs can dramatically improve the photochemical wet etching rate of p-GaP. It is also found that the enhancement of photochemical wet etching is wavelength selective. We then extended the applications of LSPRs to GaP to enhance its PL emission intensity. Finally, we prepared quasi-periodic pattern structures on GaP window layer of AlGaInP based red LEDs by photochemical laser interference etching, which can effectively enhance the light extraction efficiency of red LEDs by~70%.
Keywords/Search Tags:Photochemical wet etching, maskless parterning, localized surface plasmon resonance, photoluminescence, light emitting diodes
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