IV-VI LEAD SALT MID-INFRARED LIGHT EMITTING DEVICE DESIGN, FABRICATION AND CHARACTERIZATIONIV-VI LEAD SALT MID-INFRARED LIGHT EMITTING DEVICE DESIGN, FABRICATION AND CHARACTERIZATION

The research detailed by this dissertation has demonstrated the design, fabrication, and characterization of lead salt semiconductor mid-infrared light emitting devices. A scrupulous theoretical model has been described which estimates spectral gain from the quantum well (QW) structure based on IV-VI lead salt semiconductor material. The spectral gain of the QW structure, with both for finite and infinite well, for different crystal growth orientations is detailed. The purpose was to determine the best lead salt crystal orientation to fabricate opto-electronic devices.Detailed experimental works concerning recent developments of IV-VI lead salt light emitting devices have been demonstrated. An electrically excited QW laser on [110] oriented lead salt substrate is reported for the first time in the literature. A brief description on the fabrications and characterizations of novel microstructures in the form of rod, tube and pillar, having enormous applications in MEMS and NEMS, is provided.A theoretical exploration of spontaneous mid-infrared emission from IV-VI semiconductor photonic crystal defect microcavity is elaborated. The design is aimed to solve out challenges of the formation of resonating cavity for lead salt materials fabricated on Si(111) or BaF2(111) substrates, commonly implemented to fabricate high temperature, continuous wave (CW) lasing devices. The band structure calculations of the periodic crystal are performed using plane wave expansion (PWE) method. Finite difference (FD) perturbation correction method and finite difference time domain (FDTD) algorithms have been employed to analyze modal field distribution in the defect cavity.A study on the measurement of minority carrier lifetime, which is one of the very important figures of merit to judge opto-electronic device performance, is illustrated. Photoconductive decay (PCD) method, a very popular and well-established methodology has been adopted to carry out the experimental work. The implementation of CaF2 as a new surface passivation layer for MBE-grown PbSe single crystalline thin films on a BaF2(111) substrate has been done and the corresponding effect on device performance is compared. Minority carrier lifetimes and pulsed photoluminescence intensities from PbSe samples are observed to increase after CaF2 surface passivation. However, the improvement is comparatively more significant at low temperature than at high temperature. This may indicate that surface passivation for Pb-salt materials are not as critical as its II-VI and III-V counterparts at high temperature of device operation. Therefore, device fabrication for Pb-salt materials at elevated temperature could be relatively more cost-effective with a higher-yield

Insights into the sputter-instigated valence plasmon oscillations in CIGSe thin films

We report a unique methodology of triggering plasmonic excitations in sputtered ultrathin CIGSe films. In this approach of plasmonic excitation, secondary ion source present in the growth system instigates the formation of nanoclusters of its constituent elements, which is the source of plasmonic excitation. The formation of the nanoclusters during the growth is because of the distinct sputtering out rates of the various elements during the growth. For the verification of valence electron excitation and plasmonic oscillations, the studies performed as follows: a) investigation of electron energy loss from the ultraviolet-photoelectron spectroscopy measurements, b) quantification of the various electron energy loss contributions associated with the constituent element present in the films within the observed broad peaks in ultravoilet photoelectron spectroscopy (UPS) spectrum, c) estimation of particular plasmon contribution, i.e., particle, valence-surface, and valence-bulk plasmon at the air/thin-film interface, and within the thin film, d) verification of plasmonic behavior by analyzing different optical properties performing spectroscopic ellipsometry measurements, 5) validation of the nanocluster emergence in ultrathin CIGSe thin films deploying Field Emission Scanning Electron Microscopy. This approach is promising in terms of improving the solar cell performance parameters by supplementing the optical path length within the absorber in the broad spectral range without the need of externally supplied metal nanoparticles

Investigation of dual-ion beam sputter-instigated plasmon generation in TCOs: a case study of GZO

The use of the high free-electron concentration in heavily doped semiconductor enables the realization of plasmons. We report a novel approach to generate plasmons in Ga:ZnO (GZO) thin films in the wide spectral range of ∼1.87–10.04 eV. In the grown GZO thin films, dual-ion beam sputtering (DIBS) instigated plasmon is observed because of the formation of different metallic nanoclusters are reported. Moreover, formation of the nanoclusters and generation of plasmons are verified by field emission scanning electron microscope, electron energy loss spectra obtained by ultraviolet photoelectron spectroscopy, and spectroscopic ellipsometry analysis. Moreover, the calculation of valence bulk, valence surface, and particle plasmon resonance energies are performed, and indexing of each plasmon peaks with corresponding plasmon energy peak of the different nanoclusters is carried out. Further, the use of DIBS-instigated plasmon-enhanced GZO can be a novel mean to improve the performance of photovoltaic, photodetector, and sensing devices

Investigation of dual-ion beam sputter-instigated plasmon generation in TCOs: a case study of GZO

The use of the high free-electron concentration in heavily doped semiconductor enables the realization of plasmons. We report a novel approach to generate plasmons in Ga:ZnO (GZO) thin films in the wide spectral range of ∼1.87–10.04 eV. In the grown GZO thin films, dual-ion beam sputtering (DIBS) instigated plasmon is observed because of the formation of different metallic nanoclusters are reported. Moreover, formation of the nanoclusters and generation of plasmons are verified by field emission scanning electron microscope, electron energy loss spectra obtained by ultraviolet photoelectron spectroscopy, and spectroscopic ellipsometry analysis. Moreover, the calculation of valence bulk, valence surface, and particle plasmon resonance energies are performed, and indexing of each plasmon peaks with corresponding plasmon energy peak of the different nanoclusters is carried out. Further, the use of DIBS-instigated plasmon-enhanced GZO can be a novel mean to improve the performance of photovoltaic, photodetector, and sensing devices

Band alignment of Cd-free (Zn, Mg)O layer with Cu2ZnSn(S,Se)4 and its effect on the photovoltaic properties

Cu2ZnSn(S,Se)4 (CZTSSe) is an interesting absorber material for thin film solar cells. However, one of the key challenges for the kesterite-based solar cells is to improve the open-circuit voltage (Voc) deficit, which is resultant of recombination at the interface of buffer/absorber. In this work, Cd-free n-type buffer layers with two different Mg-doped ZnO layers (Mg0.26Zn0.74O, Mg0.30Zn0.70O) have been examined using ultraviolet photoelectron spectroscopy. The most important electronic properties which are essential for the band offset study, ie. fermi level location, valence and conduction band offsets at the interface in the CZTSSe substrate, have been determined. The conduction band offset values for Mg0.26Zn0.74O, Mg0.30Zn0.70O buffer layers has been calculated experimentally. We have also established the correlation between device parameters and performances for dual ion beam sputtered ZnO buffer/CZTSSe-based heterojunction solar cells as a function of conduction band offset and the energy distribution of interface defects, to gain deeper understanding about the Voc-deficit behavior from a high recombination rate at the buffer/kesterite interface using simulation study. From the simulation study, the values of the solar cell efficiency with Mg0.26Zn0.74O and Mg0.30Zn0.70O buffer layers are 10.18 and 10.25%, respectively, which are higher in comparison to those obtained by using conventional CdS buffer layer