Kathryn M. Kelchner

Continuous-wave Operation of AlGaN-cladding-free Nonpolar m-Plane InGaN/GaN Laser Diodes

We demonstrate continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes without Al-containing waveguide cladding layers. Thick InGaN quantum wells (QWs) are used to generate effective transverse optical mode confinement, eliminating the need for Al-containing waveguide cladding layers. Peak output powers of more than 25 mW are demonstrated with threshold current densities and voltages of 6.8 kA/cm2 and 5.6 V, respectively. The unpackaged and uncoated laser diodes operated under CW conditions for more than 15 h.

AlGaN-Cladding Free Green Semipolar GaN Based Laser Diode with a Lasing Wavelength of 506.4 nm

We demonstrate electrically driven InGaN based laser diodes (LDs), with a simple AlGaN-cladding-free epitaxial structure, grown on semipolar (2021) GaN substrates. The devices employed In0.06Ga0.94N waveguiding layers to provide transverse optical mode confinement. A maximum lasing wavelength of 506.4 nm was observed under pulsed operation, which is the longest reported for AlGaN-cladding-free III-nitride LDs. The threshold current density (Jth) for index-guided LDs with uncoated etched facets was 23 kA/cm2, and 19 kA/cm2 after application of high-reflectivity (HR) coatings. A characteristic temperature (T0) value of ~130 K and wavelength red-shift of ~0.05 nm/K were confirmed.

Blue-Green InGaN/GaN Laser Diodes on Miscut m-Plane GaN Substrate

Nonpolar blue-green (481 nm) InGaN/GaN laser diodes (LDs) were realized by using m-plane GaN substrates with a misorientation angle of approximately 1° toward [0001] direction. The laser diode structures grown on miscut m-plane GaN substrates showed significantly smoother surface morphology compared to structures grown on nominally on-axis m-plane GaN substrates. It is contributed to lower threshold current densities, longer lasing wavelength, and higher lasing yield than those on on-axis substrates grown by the same growth condition. Material improvement based on the control of substrate misorientation is essential to achieve high performance LDs beyond the blue spectral range.

Nonpolar AlGaN-Cladding-Free Blue Laser Diodes with InGaN Waveguiding

We have demonstrated AlGaN-cladding-free m-plane InGaN-based blue laser diodes (LDs) using a novel structure that employs 50-nm-thick n- and p-type InxGa1-xN (x = 5–10%) as waveguiding layers. The thick, high In content InGaN waveguiding layers provided significant refractive index contrast to the GaN cladding layers, thereby eliminating the need for AlGaN cladding. Under pulsed operation, lasing was achieved at 442 nm with a threshold current density of 10 kA/cm2.

Polarized light extraction in m-plane GaN light-emitting diodes by embedded photonic-crystals

The polarization-preserving property of photonic crystals (PhCs) is combined to the superior extraction efficiency of embedded PhCs to enhance polarized light emission in m-plane GaN light-emitting diodes. As guided modes in m-plane GaN are mostly polarized along the a-direction (E∥a), their efficient extraction is achieved by one-dimensional embedded PhCs also aligned to the a-direction. A better diffraction efficiency is obtained by air-gap PhCs which required the growth of high quality, defect-free, m-plane GaN coalesced over the embedded air-grooves.

Optical properties of extended and localized states in m-plane InGaN quantum wells

Scanning near-field and time-resolved photoluminescence spectroscopy were applied to study potential fluctuations and photoexcited carrier dynamics in single m-plane InGaN quantum well structures. The far- and near-field spectra were found to have contributions from transitions to the first and second hole levels in the extended states, and transitions in the localized states. Correlations between parameters of the near-field spectra confirmed that extended state luminescence was prevailing. The localized states, which were found to be separated from the extended states by ∼10 meV barriers, were attributed to regions of a higher In content.

Continuous-Wave Operation of Pure Blue AlGaN-Cladding-Free Nonpolar InGaN/GaN Laser Diodes

We present the first reported continuous-wave (CW) operation of pure blue AlGaN-cladding-free (ACF) nonpolar m-plane InGaN/GaN laser diodes (LDs). CW lasing was achieved at a wavelength of 461 nm and a threshold current density of 4.1 kA/cm2 for LDs with an InGaN-based separate confinement heterostructure (SCH) waveguide design. The devices showed a 9 nm/decade blue-shift of spontaneous emission wavelength with increasing current density, a characteristic temperature of 156 K, a red-shift with increasing stage temperature of 0.05 nm/K, and an estimated thermal impedance of 60 K/W.

InGaN/GaN Blue Laser Diode Grown on Semipolar (3031) Free-Standing GaN Substrates

We demonstrate the first electrically-injected InGaN/GaN laser diodes (LDs) grown on semipolar (3031) free-standing GaN substrates. The lowest threshold current density (Jth) was 5.6 kA/cm2 with a clear lasing peak at 444.7 nm. The peak electroluminescence (EL) wavelength blue-shifted 4 nm below threshold and the characteristic temperature was ~135 K. These results suggest that the semipolar (3031) plane may be a potential candidate for growing high performance nitride-based LDs.

m-Plane GaN-Based Blue Superluminescent Diodes Fabricated Using Selective Chemical Wet Etching

An m-plane-GaN based blue superluminescent diode was demonstrated utilizing the asymmetric chemical properties of the ±c facets. The non-reflecting -c plane facet, intended to prevent optical feedback along the c-axis waveguide, was fabricated by KOH wet etching. KOH selectively etched the cleaved -c facet leading to the formation of hexagonal pyramids without etching the +c facet. The peak wavelength and full width at half max were 439 and 9 nm at 315 mA, respectively, with an output power of 5 mW measured out of the +c facet.

Pulsed high-power AlGaN-cladding-free blue laser diodes on semipolar (202¯1¯) GaN substrates

We demonstrate high-power AlGaN-cladding-free blue laser diodes (LDs) on semipolar (202¯1¯) GaN substrates with peak output powers and external quantum efficiencies (EQEs) that are comparable to state-of-the-art commercial c-plane devices. Ridge waveguide LDs were fabricated on (202¯1¯) GaN substrates using InGaN waveguiding layers and GaN cladding layers. The devices lased at 454 nm at room temperature. We measured an output power of 2.15 W, an EQE of 39%, and a differential quantum efficiency of 49% from a single facet with a pulsed drive current (current density) of 2.02 A (28.1 kA/cm2).