There are two sections in this thesis, the first section we measured the photoluminescence (PL) spectra¡Bphotocurrent spectra and electro absorption spectra of InGaAsN single quantum well structures grown by MBE. From temperature-dependent PL spectra of InGaAsN, we observed a localized level at low temperature, and the carrier localization effect increases when the mole fraction of nitrogen increases (2.1%~3.25%). This peculiarity influences the PL peak position and the PL linewidth, and it can be improved by adequate annealing. We also obtained the activation energies about 52~59meV by Arrhenius plot and thermal quenching model. For the photocurrent spectra we observe the sub-band transition and quantum confined stark effect. From the electro-absorption spectra, we obtain the maximum absorption changes (

In this thesis, we have set up a SiO2 sputter system. The system includes sputter gun, RF power supply, RF power controller, turbo pump, quick access door, cooling water tubes, gas lines, electric circuits etc. We applied sputter techniques for quantum well intermixing (QWI) process. We can adjust the pressure, gas, RF power etc. of the sputter system to fit the best QWI conditions and then sputter a SiO2 film on the samples. The samples with multiple quantum wells were grown by our team members using molecular beam epitaxy system. After SiO2 film deposition, the samples were annealed by Rapid Thermal Process. The annealing temperatures are about 650¢J-750¢J. Following the thermal annealing, room-temperature PL measurements were used to study the blue shift and intensity change after QWI process. After our hard working, we had fixed many problems of sputter system. We have obtained useful data through many QWI experiments. Our results are listed as follows : PL intensity : We use RF power = 100W, sputter time = 5 min., annealing temperature = 675¢J, annealing time = 30 sec. PL intensity has been enhanced by 25 times. Blue shift : there is no clear blue shift.

In this thesis, we have set up a SiO2 sputter system. We applied sputter techniques for quantum well intermixing (QWI) process to increase the bandgap of the quantum well structure. The samples with multiple quantum wells were grown by our team members using molecular beam epitaxy system, and the MQW structure were grown by MOCVD. Before sputtering, some samples will use ICP to enhance the vacancy on the surface. First, we will sputter SiO2 on the surface of sample. After SiO2 film deposition, the samples were annealed by Rapid Thermal Process. And ordinary annealing were about 700¢J~800¢J. A later period, the annealing temperatures will be above 850¢J. Room-temperature PL (Photoluminescence) measurements were used to study the blue shift and intensity change after QWI process. And we will do the mesa process to measure the characteristic of optoelectronics. If the conditions are RF power = 100W, sputter time = 30 min, ICP enhance 250W for 2 min, annealing temperature = 825¢J, annealing time = 60 sec. The PL signal have a blue shift of 64nm(wavelength from 1506nm to 1444nm).When annealing temperature =700¢J, and annealing time = 60 sec, we have a blue shift of 12nm(wavelength from 1572nm to 1560nm) on the C116 sample. We do the mesa process on the MQW which contain P and it have a large blue shift. After the process, we success to compare the different between EL and Photocurrent. But the structure of samples which certain Al do not have a apparent blue shift. And the annealing temperature is too large, samples will be damaged. We think that the reason have relation to materials of the sample.

Abstract In this thesis, we have setup a photoluminescence (PL) measurement system to investigate the quantum well intermixing (QWI) effects on semiconductor multiple quantum-well (MQW) structures. The measured samples include 1.3mm and 1.55mm InGaAsP MQW laser structures grown by MOCVD, and 1.55mm InGaAlAs MQW structures by MBE. The QWI process was performed by rapid thermal annealing at 600¢J~800¢J in 1 min with a ~1300Å SiO2 layer sputtered on the semiconductor surface. Following the SiO2 sputtering and thermal annealing, room-temperature PL measurements were used to study the QWI effect. The result shows that the PL intensity is reduced for the MOCVD samples, while the MBE samples have up to 47 times increase of PL intensity. After QWI process, all the samples have a blue-shift in PL spectra. The 1.55mm InGaAsP laser structures by MOCVD have a maximum blue-shift of 34nm, and the MBE samples of 12nm after 800¢J annealing.

Abstract We have applied PID and IFVP techniques to modify semiconductor bandgap in quantum well and quantum dot to achieve quantum well intermixing (QWI) and quantum dot intermixing (QDI). In quantum well intermixing experiment, we combine inductively coupled plasma reactive ion etching (ICP-RIE) and sputtering 300nm SiO2 to induce defects. And then, after high temperature annealing by RTA, we observed the results by using PL measurement. The samples used in this study were grown by molecular beam epitaxy(MBE) and consists of triple In0.53Ga0.47As/In0.53Ga0.26Al0.21As quantum wells. We used Ar+ bombardment on samples by ICP-RIE for 5 minutes, and then sputtered a 300nm SiO2 capping layer upon the samples. Finally the sample was annealed at 800¢J for 1 minutes. After the process, we got 150nm blue-shift (1575~1425nm) by measurement PL spectrum and applied XRD fitting to simulate 140nm blue-shift (1580~1440nm).On the same process step, we increased ICP-RIE bombardment time to 7 minutes thus we observed largest 269nm blue-shift from PL spectrum. InAs/In0.52Al0.48As,In0.95Al0.05As/In0.52Al0.48As,and In0.95Ga0.05As/In0.52Al0.48As quantum dot structures were grown by MBE. In0.95Ga0.05As/In0.52Al0.48As quantum dot structure has larger blue-shift by sputtering 300nm SiO2 and annealing at high temperature by RTA. We got 282nm blue-shift annealing at 800¢J for In0.95Ga0.05As/In0.52Al0.48As quantum dot structure. Furthermore, we got largest 366nm blue-shift when we etched the thickness of capping layer and annealed at 800¢J.

The band-gap engineering is an important technique for integration of optoelectronic devices. Using the inter-diffusion of atoms in the quantum well structure, Quantum-Well Intermixing (QWI) technique has been widely used for band-gap engineering due to its simple process and capability of local tuning in chip. Electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) are two essential devices in optoelectronic field. The band-gap engineering is needed to get optimized performance in integration of EAM and SOA because of the energy level offset in both material structures. In this work, an simple QWI technique, called impurity free vacancy diffusion (IFVD), is employed to integrate EAM and SOA. In the device design, a chain structure of EAM-integrated SOA is used for high-speed and low-noise performance. No re-growth step is needed in the whole device process. An good property EAM with blue shift of 20nm from SOA portion is achieved from this IFVD method.

In this work, a quantum well intermixing(QWI) technology, called impurity free vacancy diffusion(IFVD), is used to do the bandgap engineering in an optoelectronic monolithic integration. The monolithic integration of SOAs and EAMs is taken as an example. By IFVD, the transition energy levels of EAM quantum wells can be shifted to shorter wavelength regime, while SOA quantum wells are kept the same. Therefore, the overall SOA-integrated EAM efficiency can be improved. A 400nm thick SiO2 is sputtered at the EAM regions to locally create defects in the surface of pin InGaAsP/Imp layer structure. Rapid thermal Annealing (RTA) technique at 850oC is then used to inter-diffuse the atom of quantum wells. A SOA-integrated EAM is fabricated on such template. Ti/Pt/Au and Ni/AuGe/Ni/Au are used for p-type and n-type metallization. An optical waveguide structure is defined by selective undercut-etching active region. The PMGI is spun for planarization and bridging. A Ti/Au is finally deposited as microwave coplanar waveguide. A DC measurement of photocurrent spectrum is performed to examine the wavelength shift. A 10nm shift is found between EAM and SOA regions. Modulation efficiency of 15dB/V with extinction ratio of higher than 20dB is observed in EAM device. And the optical gain of SOA is found as 3dB at 1540nm excitation wavelength. -3dB bandwidth of 20GHz is obtained. In comparison with sample without intermixing, the same results are achieved in intermixing sample, suggesting no regrowth processing is needed for obtaining the same quality of optoelectronic integration.

Laser Diodes (LD) have numerous applications for industry, military, medicine and communications. The first visible LD was invented in 1962 by Nick Holonyak, emitted at 710 nm (red). In 1990s, Shuji Nakamura invented the blue and green Light Emitting Diodes (LED) and later LDs. The production of LDs emitting between 532- 632 nm has been severely lagging behind the rest of the visible spectrum. Yellow and orange LDs are still not accessible due to the lack of successfully grown material with high optical efficiency. AlGaInP is the quaternary compound semiconductor used to grow green to red LEDs and red LDs. At a material composition that is supposed to lase below 630 nm, the optical efficiency becomes low due to the oxygen-related defects associated with high Al content. The quantum well intermixing (QWI) is a post-growth process that is applied to laser structure to tune the wavelength of laser. Until now, there are limited reports on successful intermixing of InGaP/InAlGaP laser structures while maintaining the crystal quality. In this work, we introduced a novel intermixing process that utilizes the high strain induced by the dielectric film during annealing to initiate the intermixing. We deposited SiO2 capping by plasma-enhanced chemical vapor deposition (PECVD) onto the InGaP/InAlGaP laser structure emitting at 635 nm, and then annealed the structure up to 950 Celsius for different periods of time, resulting in an astonishing 100 nm blueshift. This blueshift allowed us to produce an unprecedented shorter wavelength orange lasers emitting at 608 nm. For low degree of intermixing, we have noticed an increase in the intensity of the photoluminescence (PL) signal. The improvement in the PL signal was translated to a reduction in threshold current. We implemented the technique on an LED structure with Al-rich QWs emitting at 590 nm. Significant increase in the PL intensity (20 folds) was observed. By analyzing the improved structure, we observed reduction in oxygen contamination. This may represent a solution to the oxygen-related defect. The thesis opens the door for major steps forward in GaInP/AlGaInP structures for manufacturing efficient optoelectronic devices in the green, yellow and orange visible range.

Computed Tomography (CT) is a medical imaging modality which acquires anatomical data via the unique x-ray attenuation of materials. Yet, some clinically important materials remain difficult to distinguish with current CT technology. Spectral CT is an emerging technology which acquires multiple CT datasets for specific x-ray spectra. These spectra provide a fingerprint that allow materials to be distinguished that would otherwise look the same on conventional CT. The unique characteristics of spectral CT data motivates research into novel visualization techniques. In this thesis, we aim to provide the foundation for visualizing spectral CT data. Our initial investigation of similar multi-variate data types identified intermixing as a promising visualization technique. This promoted the development of a generic, modular and extensible intermixing framework. Therefore, the contribution of our work is a framework supporting the construction, analysis and storage of algorithms for visualizing spectral CT studies. To allow evaluation, we implemented the intermixing framework in an application called MARSCTExplorer along with a standard set of volume visualization tools. These tools provide user-interaction as well as supporting traditional visualization techniques for comparison. We evaluated our work with four spectral CT studies containing materials indistinguishable by conventional CT. Our results confirm that spectral CT can distinguish these materials, and reveal how these materials might be visualized with our intermixing framework.

The three wave mixing process was modeled in GaAs:AlGaAs superlattices using two new modeling tools that were developed in the course of this work: A 2D beam propagation tool for optimizing quasi-phase matching gratings, and a 1D iterative beam propagation tool for determining the output powers and threshold of optical parametric oscillators of arbitrary geometries. The 2D tool predicts close to 80% enhancement of conversion e ciency by phase matching near 800 nm compared to 775 nm, which was the originally designed operation wavelength. The model also predicts resonant behaviour for an abrupt grating pro le. The 1D tool was used to determine the threshold conditions for para- metric oscillation for di erent geometries. The performances of di erent phase matching approaches in AlGaAs were quantitatively compared. The model also indicated the need for pulsed operation to achieve reasonably low threshold powers in AlGaAs waveguides.