A. Garg

Semiconductor Quantum Dot Lasers: A Tutorial

Semiconductor quantum dot lasers have been extensively studied for applications in future lightwave telecommunications systems. This paper summarizes a tutorial that was presented at the Optical Fiber Communication (OFC) 2010. The motivation for quantum dots in lasers is outlined, and the desirable effects of three dimensional quantum confinement are described. Methods for forming self-assembled quantum dots and the resultant laser characteristics are presented. The formation of patterned quantum dot lasers and the results of this type of quantum dot laser are outlined. Finally, a novel inverted quantum dot structure or nanopore laser containing 3-D quantization formed from an engineered periodicity is introduced.

Measurements of the complex refractive index of Pd and Pt films in air and upon adsorption of H 2 gas

We present complex refractive index measurements of Pd and Pt films from 700-1700 nm using variable angle spectroscopic ellipsometry. Refractive index changes upon H2 gas adsorption were determined by measuring normal incidence reflection and transmission.

Directed self-assembly of InAs quantum dots on nano-oxide templates

We describe the growth and characterization of InAs quantum dots on SiO2 patterned GaAs by metal organic chemical vapor deposition. Arrays of quantum dots with densities as high as 1.8×1010 cm−2 fabricated by electron beam lithography are demonstrated. A process consisting of dry and wet etching to minimize etch damage is developed. As the mask diameter increases, the nucleation transitions from single dots to multidot clusters. We achieve more uniform size and shape distributions of dots on patterned regions relative to unpatterned dots as revealed by structural characterization and room temperature photoluminescence emission spectra.

Photon antibunching from a single lithographically defined InGaAs/GaAs quantum dot

We demonstrate photon antibunching from a single lithographically defined quantum dot. Measurement of the second order autocorrelation function indicates g(2)(0) = 0.395 ± 0.030, below the 0.5 limit necessary for classification as a single photon source.

Experimental verification of reduced intersubband scattering in ordered nanopore lattices

A photoluminescence study of emission from a periodically perforated quantum well at 77 K is presented. Good agreement is observed between numerical predictions and experimental results. The effects of pore diameter on peak emission wavelength and relative emission from second excited subbands are analyzed. The results are found to be consistent with predictions of reduced intersubband scattering rate in nanopore lattices due to the reduced wave function overlap between the initial and final states arising from the in-plane periodicity.

A single spectral mode wide stripe laser with very narrow linewidth

We present results on a single spectral mode wide stripe semiconductor laser with an integrated surface etched distributed Bragg reflector operating at 975 nm with very narrow linewidth. Linewidths as low as 220 kHz have been obtained from a 40 μm wide stripe laser. For 980 nm devices reporting a linewidth of sub-1 MHz, the power of 0.5 W (linewidth of 350 kHz) is the highest obtained at this wavelength.

Wide-Stripe Distributed Bragg Grating Lasers With Very Narrow Spectral Linewidth

Gain-guided lasers with distributed Bragg reflector gratings that exhibit narrow emission linewidths of under 500 kHz are demonstrated. Partial coverage of a facet with a grating is found to be sufficient to ensure single-wavelength laser operation. Narrow linewidth operation in 40 and 150-μm wide lasers with partial gratings is demonstrated. The use of antireflection coatings to suppress spurious Fabry-Perot modes is also presented. Linewidths as low as 200 kHz that are insensitive to drive current are observed.

Time-resolved photoluminescence of lithographically defined quantum dots fabricated by electron beam lithography and wet chemical etching

We measure the time-resolved photoluminescence characteristics of a novel type of lithographically patterned quantum dot fabricated by electron beam lithography, wet chemical etching, and overgrowth of the barrier layers by metalorganic chemical vapor deposition.We find that the quantum dot (QD) photoluminescence exhibits a bi-exponential decay that we explain in terms of the fast capture of carriers by defect states followed by a slower radiative relaxation process. We also perform a systematic investigation of the rise time and decay time as a function of the QD density, size, and temperature. These measurements indicate that the carrier capture process in this type of QD is limited by carrier drift within the GaAs barrier material.

Highly uniform periodic inverse quantum dots arrays

We demonstrate high density, periodic arrays of inverse quantum dots with ±1 nm (σ_d/d = 0.025) variation of the critical dimension. The effect of this variation on the energy dispersion and intersubband gap is evaluated.

Narrow linewidth operation in broad area laser diodes

We present a design that achieves single spectral mode, narrow linewidth operation in broad area diodes. To the best of our knowledge, for 980 nm devices reporting a linewidth of sub-1 MHz, the power of 0.5 W (linewidth of 350 kHz) is the highest obtained.