OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 2016
There is strong interest in minimizing the volume of lasers to enable ultracompact, low-power, co... more There is strong interest in minimizing the volume of lasers to enable ultracompact, low-power, coherent light sources. Nanowires represent an ideal candidate for such nanolasers as stand-alone optical cavities and gain media, and optically pumped nanowire lasing has been demonstrated in several semiconductor systems. Electrically injected nanowire lasers are needed to realize actual working devices but have been elusive due to limitations of current methods to address the requirement for nanowire device heterostructures with high material quality, controlled doping and geometry, low optical loss, and efficient carrier injection. In this project we proposed to demonstrate electrically injected single nanowire lasers emitting in the important UV to visible wavelengths. Our approach to simultaneously address these challenges is based on high quality III-nitride nanowire device heterostructures with precisely controlled geometries and strong gain and mode confinement to minimize lasing thresholds, enabled by a unique top-down nanowire fabrication technique.
ABSTRACT We obtained single-mode lasing in GaN nanowires by using a limited number of cavity mode... more ABSTRACT We obtained single-mode lasing in GaN nanowires by using a limited number of cavity modes and a narrow gain spectra. The fabrication was achieved by a top-down technique in high quality GaN films.
ABSTRACT We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial In... more ABSTRACT We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial InGaN semiconductor thin films using a narrowband laser with a linewidth less than ∼1 nm. In the initial stages of PEC etching, when the thin film is flat, characteristic voltammogram shapes are observed. At low photo-excitation rates, voltammograms are S-shaped, indicating the onset of a voltage-independent rate-limiting process associated with electron-hole-pair creation and/or annihilation. At high photo-excitation rates, voltammograms are superlinear in shape, indicating, for the voltage ranges studied here, a voltage-dependent rate-limiting process associated with surface electrochemical oxidation. As PEC etching proceeds, the thin film becomes rough at the nanoscale, and ultimately the self-limiting etch kinetics lead to an ensemble of nanoparticles. This change in InGaN film volume and morphology leads to a characteristic dependence of PEC etch rate on time: an incubation time, followed by a rise, then a peak, then a slow decay.
Stable single-mode lasing operation from a pair of coupled GaN nanowires is demonstrated through ... more Stable single-mode lasing operation from a pair of coupled GaN nanowires is demonstrated through optical pumping. GaN nanowires with different lengths were placed side-by-side in contact to form a coupled cavity through nanoprobe manipulation. Unlike individual nanowire lasers, which operate in a combined multiple transverse and multiple longitude mode oscillation, a coupled nanowire-pair provides a mode selection mechanism through the Vernier effect, which can strongly enhance the free spectrum range between adjacent resonant modes and generate a stable single-mode operation with a high side-mode suppression ratio.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Jun 1, 2011
ABSTRACT We study lasing in individual top-down fabricated GaN nanowires by optical pumping. We o... more ABSTRACT We study lasing in individual top-down fabricated GaN nanowires by optical pumping. We observe single mode emission with a side mode suppression of 15 dB, linewidths of less than 1 nm and thresholds as low as 250 kW/cm2.
Lighting applications are presently limited by the lack of efficient LEDs across the visible spec... more Lighting applications are presently limited by the lack of efficient LEDs across the visible spectrum. We review materials challenges that underlie the ldquogreen-yellow gaprdquo in LED efficiency and describe emerging approaches for bridging that gap.
We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lase... more We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architectu...
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 2016
There is strong interest in minimizing the volume of lasers to enable ultracompact, low-power, co... more There is strong interest in minimizing the volume of lasers to enable ultracompact, low-power, coherent light sources. Nanowires represent an ideal candidate for such nanolasers as stand-alone optical cavities and gain media, and optically pumped nanowire lasing has been demonstrated in several semiconductor systems. Electrically injected nanowire lasers are needed to realize actual working devices but have been elusive due to limitations of current methods to address the requirement for nanowire device heterostructures with high material quality, controlled doping and geometry, low optical loss, and efficient carrier injection. In this project we proposed to demonstrate electrically injected single nanowire lasers emitting in the important UV to visible wavelengths. Our approach to simultaneously address these challenges is based on high quality III-nitride nanowire device heterostructures with precisely controlled geometries and strong gain and mode confinement to minimize lasing thresholds, enabled by a unique top-down nanowire fabrication technique.
ABSTRACT We obtained single-mode lasing in GaN nanowires by using a limited number of cavity mode... more ABSTRACT We obtained single-mode lasing in GaN nanowires by using a limited number of cavity modes and a narrow gain spectra. The fabrication was achieved by a top-down technique in high quality GaN films.
ABSTRACT We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial In... more ABSTRACT We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial InGaN semiconductor thin films using a narrowband laser with a linewidth less than ∼1 nm. In the initial stages of PEC etching, when the thin film is flat, characteristic voltammogram shapes are observed. At low photo-excitation rates, voltammograms are S-shaped, indicating the onset of a voltage-independent rate-limiting process associated with electron-hole-pair creation and/or annihilation. At high photo-excitation rates, voltammograms are superlinear in shape, indicating, for the voltage ranges studied here, a voltage-dependent rate-limiting process associated with surface electrochemical oxidation. As PEC etching proceeds, the thin film becomes rough at the nanoscale, and ultimately the self-limiting etch kinetics lead to an ensemble of nanoparticles. This change in InGaN film volume and morphology leads to a characteristic dependence of PEC etch rate on time: an incubation time, followed by a rise, then a peak, then a slow decay.
Stable single-mode lasing operation from a pair of coupled GaN nanowires is demonstrated through ... more Stable single-mode lasing operation from a pair of coupled GaN nanowires is demonstrated through optical pumping. GaN nanowires with different lengths were placed side-by-side in contact to form a coupled cavity through nanoprobe manipulation. Unlike individual nanowire lasers, which operate in a combined multiple transverse and multiple longitude mode oscillation, a coupled nanowire-pair provides a mode selection mechanism through the Vernier effect, which can strongly enhance the free spectrum range between adjacent resonant modes and generate a stable single-mode operation with a high side-mode suppression ratio.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Jun 1, 2011
ABSTRACT We study lasing in individual top-down fabricated GaN nanowires by optical pumping. We o... more ABSTRACT We study lasing in individual top-down fabricated GaN nanowires by optical pumping. We observe single mode emission with a side mode suppression of 15 dB, linewidths of less than 1 nm and thresholds as low as 250 kW/cm2.
Lighting applications are presently limited by the lack of efficient LEDs across the visible spec... more Lighting applications are presently limited by the lack of efficient LEDs across the visible spectrum. We review materials challenges that underlie the ldquogreen-yellow gaprdquo in LED efficiency and describe emerging approaches for bridging that gap.
We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lase... more We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architectu...
Uploads