Research

Students: Evan Pickett
Description: The dilute nitrides are a class of semiconductor alloys, usually III-V materials such as GaAs or GaP, that contain 0-5% nitrogen. As an alloy element, nitrogen induces a large band bowing parameter, reducing both the band gap and the lattice constant. Alloying with indium, while manipulating composition to achieve precise strain or lattice match, can extend the band edge as low as 800 meV. The MBE growth of these alloys requires careful control and characterization, including TEM and XRD. XRD yields an excellent overview of layer crystallinity and uniformity, while brightfield and darkfield TEM imaging can reveal nanoscale strain and composition variations.

Students: Yijie Huo, Hai Lin, Yiwen Rong
Description: The focus of this project is to grow group IV (Si/Ge/Sn) semiconductor by MBE. The main target is to achieve a direct or near direct bandgap semiconductor which can be used to build CMOS compatible laser.

Students: Cheng Han Yang

Students: Naga Phani Aetukuri

Students: Angie Lin
Description: The focus of this project is to develop artificially structured materials with simultaneously enhanced nonlinear optical properties and a periodic modulation of the sign of the non-linear coefficient which provides phase match to optical signals of different frequency. This project has two primary foci; one for waveguide devices that can be integrated into optical networks for a variety of non-linear functions, such as all optical channel switching, and the second for thick bulk-patterned materials for high power laser generation in the mid-IR and Terahertz regions where there are no available compact solid state or semiconductor laser sources.

Students: Yijie Huo
Description: The focus of this project is to produce an electrically pumped, silicon based laser. There are two major thrusts, a) to create SiGe based quantum well and/or quantum dot active regions in which the material is either direct or nearly direct bandgap and b) Si based photonic crystal cavities with ultra-high Q to eliminate any photonic states for spontaneous emission and enable stimulated emission into the single allowed state of the photonic crystal cavity.

Students: Zhilong Rao (former)
Description: The focus of this research project is to develop high-intensity nano-aperture VCSELs for ultrahigh-resolution near-field imaging and ultrahigh-density near-field optical data storage. We have demonstrated record-high intensity nano-aperture VCSELs with sub-100nm near-field spot sizes using ridge nanoapertures including bowtie, C, H and I-shaped apertures. The next step is to develop the application of these high-intensity nano-aperture VCSELs for near-field imaging and optical data storage.

Students: Xiao Hann Lim
Description: This work involves the development of a highly stable evanescently-coupled fiber semiconductor laser system and optimizing it for higher performance and efficiency. This is a design that uses the principle of evanescent waveguide coupling as an alternative to free-space coupling, to connect the source (the semiconductor laser) to the transmission medium (optical fiber). Due to the structure and construction of the laser, the output beam shape is elliptical, whereas optical fibers are circular. If these two components are directly joined together, due to the mismatch of the mode shapes, a large amount of light is lost, which is highly undesirable since this may translate to lost information. One of the ways to solve the problem is the use of free space direct coupling, making use of asymmetrical lenses in order to match the elliptical output beam of the laser to the circular shape of the fiber. However this requires precise placement and alignment of the components, which increases the cost of packaging significantly. Previous students of the Harris group have come up with the idea of using ARROW (Anti-resonant reflective optical waveguides) and evanescent wave coupling in order to alleviate this problem of complexity in the external lens optics. Compared to free space direct coupling, the main benefits of evanescent coupling are more relaxed alignment tolerances, simpler packaging, higher immunity to catastrophic mirror damage and higher spectral purity.

Students: Jun Pan
Description: The focus of this project is to develop photonic crystal based devices for stopping light all-optically. Dynamic resonator system has been used to accommodate the light pulse, compress the bandwidth and correspondingly drastically slow down the propagation speed of light. As a result of this all-optical manipulation, it has profound implication for coherent store of light pulse and ultimate control of light. Current work focuses on the e-beam lithography and etching fabrication process.

Students: Hopil Bae, Tomas Sarmiento
Description: Our work has focused on developing GaInNAsSb on GaAs where we have realized the lowest threshold current 1.55μm edge-emitting lasers and the first monolithic 1.55μm VCSELs. GaInNAsSb is a metastable material with many challenges to realize the longer wavelengths, but the tremendous advantages of producing long wavelength devices on GaAs where excellent DBR mirror technology exists and the potential to integrate photonic crystal waveguides and resonators will enable integration of more functional photonic integrated circuits, arrays of much lower cost, 2-D lasers and modulators which can be easily coupled into fiber or utilized in free space architectures and offer great architectural diversity. Edge emitting lasers from these alloys also offer much greater opportunity to realize very high power semiconductor laser pumps for Raman amplifiers and semiconductor optical amplifiers to open up the entire 1.3-1.6μm low loss fiber region as well as provide resonant pumps for very high power, high efficiency solid-state lasers. We achieved very low threshold current density of 373 A/cm2 for 1.55μm edge-emitting lasers and the first GaAs-based monolithic VCSEL at 1.53μm.

Students: Yangsi Ge
Description: The focus of this project is to provide optical modulator on silicon for high-speed communication and interconnects with CMOS-compatible fabrication. The growth and optical characterization of Ge/SiGe quantum wells on silicon substrates are being investigated to exploit its strong quantum confined Stark effect for electroabsorption modulator in long wavelength regime. The modulator and detector array based on this approach will enable all-group-IV photonics integrated with electronics.

Students: Mathilde Gobet
Description: This work focuses on the simulation, fabrication and characterization of VCSELs at 1.55 μm with GaInNAsSb quantum wells. The aims of this project are to realize electrically pumped continuous wave VCSELs on GaAs at 1.55 μm, as well as VCSEL arrays for optical communications and wavelength division multiplexing applications. The first part of this project consists of improving the laser characteristics, namely by decreasing the threshold current and operating voltage to obtain CW operation, extending the wavelength to 1550 nm, as well as developing and optimizing new fabrication steps. The second part of this project involves the realization of high-speed devices with advanced fabrication techniques and the fabrication of multiple-wavelength VCSEL arrays with wavelength spacing on the order of 0.4 nm to use with DWDM technologies.

Students: Meredith Lee
Description: Description: This project focuses on the development of a miniaturized, "label-free" sensor for lab-on-a-chip biomedical, bio-defense, and environmental monitoring applications. The sensor features a 2D photonic crystal slab (sub-wavelength grating) that gives rise to a guided resonance when illuminated by normally-incident light. When molecules bind to the photonic crystal slab, the spectral location of the resonance shifts. We can detect this by sweeping the wavelength of the incident light.

Silicon Nitride photonic crystal slabs were fabricated on quartz substrates using optical holography. The design targets operation in the near-infrared transparency window, for low absorption of water and hemoglobin. Initial measurements agree with 3D Finite Difference Time Domain simulations, and demonstrate the detection of index changes on the order of 10^-3 for bulk aqueous solutions. Present work includes the integration of microfluidic controls and the design/simulation of new sensor architectures for increased sensitivity. We ultimately aim to combine multiple sensing mechanisms on one platform to provide rapid, correlated bio-analysis. This is a collaboration with the Center for High Technology Materials (CHTM) at the University of New Mexico.

Students: Thomas O'Sullivan
Description: We are fabricating miniaturized, integrated optical (VCSEL/detector) fluorescence sensors for live tissue imaging in unanesthetized mice. Major challenges of this project include fabricating detectors with extremely low dark current and sufficiently blocking laser excitation background from saturating the detector. This project also involves the simulation and modeling of light interaction with live tissue. The devices will ultimately be implanted in freely moving mice to study tumor growth and cancer stem cell dynamics. This is a collaborative project with the School of Medicine.

Students: Thomas Lee
Description: Our current research centers on the development of integrated optical sensors for functional brain imaging. Intensity changes in back-scattered light, called Intrinsic Optical Signals (IOS) track hemodynamic changes associated with neural activity. Current imaging systems typically employ benchtop equipment including lamps and CCD cameras to study anesthetized animals using visible wavelengths. Sensor integration using arrays of semiconductor sources and detectors operating in the near-infrared (700-850nm) will allow studies of freely behaving animals and the potential for long-term, minimally invasive neuroscience studies. Other possible applications include pharmaceutical evaluation and neural prosthetics. Current work involves studying the characteristics of near-infrared IOS through skull, exploring ways to take advantage of structured illumination to improve performance, and characterization of low-frequency noise in VCSELs. Planned work includes a macro-scale prototype to test candidate designs and exploration of lower-cost detection devices (e.g. CMOS image sensors.)

Students: Justin Brockman

Students: Li Gao, Larkhoon Leem
Description: The focus of this program is to develop new device concepts utilizing the spin of electrons rather than charge for current. The immediate focus is developing injection of spin polarized electrons into GaAs using ferromagnetic metal Schottky barriers and to detect spin polarized electrons using recombination from quantum wells or quantum dots. The longer range interest is to investigate coherence lifetimes, storage and manipulation of spin polarized electrons for a variety of new electron devices and as potential application to quantum computing.

Students: Yiwen Rong
Description: The purpose of this research is to use Si compatible technology to enable sillicon photonics for computation and communication. The focus is the design and fabrication of photonic devices based on Si/Ge structures with QCSE. We use molecular beam epitaxy technology for thin film deposition and use standard CMOS compatible process to fabricate the devices.

Students: Barden Shimbo
Description: I am developing a novel fabrication process for single electron tunneling devices. Using current-induced local oxidation, I isolate gold islands in a thin titanium oxide strip between adjacent, lateral titanium leads. The process relies on aspects of self-assembly, self-alignment, and self-limitation to attempt to meet the stringent fabrication requirements. This project has also involved device simulation and low-temperature electrical measurements.

Students: Donghun Choi
Description: The focus of this research is to analyze the interface between III-V compound semiconductors and high-k gate oxide and fabricate III-V MOS FET using them. Since some compound semiconductor such as InGaAs, GaAs or InSb showed relatively higher electron mobility than Si, we want to improve device performance by using high mobility channel layer grown by MBE. Optional surface treatments are tried to reduce interface defects before ALD high-k deposition. In addition, we're trying to grow III-V compound semiconductors on Si substrate using Ge buffer layer. Pure Ge growth on Si substrate by reduced-pressure CVD has been carried out to achieve acceptable property.

Students: Paul Lim

Students: Evan Pickett
Description: Inorganic solar cells can be structured to increase absorption, minimize reflection, and maximize efficiency. The goal of this project is to see if nanostructuring the absorber layer can yield an increase in efficiency by increasing carrier collection, while also searching for new low-cost materials to compete with traditional Si or CIGS technologies. Ideally, the results of nanostructuring simulations could be applied towards evaluating suitable new candidate materials such as CZTS.