Quantum-well and quantum-dot superluminescent diodes operating at 1.55 μm at high power have been developed. An optical output power of more than 600 mW in pulsed mode was produced from the device having 8 identical quantum-wells at room temperature, corresponding to the wall-plug efficiency of 28%. A continuous wave power was 26 mW (p-side up mounting) and the spectral modulation depth was 15% over the entire emission spectral width of 25 nm. For a device with 5 non-identical quantum-wells, a 255-nm spectral width centered at 1.55 μm was achieved. For a device with 5 closely identical layers of quantum-dots the gain medium exhibited a spectral width of 181 nm around 1.55 μm.
We have investigated the characteristics of 1550 nm GaInAsP/InP multiple quantum well (MQW) structures to be used as the gain medium in monolithic mode-locked lasers. For this purpose, a series of laser structures with 3 QWs, 5 QWs and 8 QWs were grown and processed into ridge waveguide lasers. The impact of the quantum well number was studied by analyzing the changes in threshold current, external quantum efficiencies, gain-spectra and linewidth enhancement factors, which are valuable in design and modeling of the mode-locked lasers. Monolithic 20 GHz mode-locked lasers were fabricated. Pulse trains with a good extinction ratio of 14.8 dB and less than 14 ps in width were demonstrated, and an average power of 1 mW could be coupled into an optical fiber.
We report the growth of GaInAsN heterostructures on GaAs substrates by conventional molecular beam epitaxy (MBE) using a radio frequency plasma source. Lattice-matched bulk samples and several strained single quantum well (SQW) and multiple quantum well (MQW) structures were grown. The QWs were sandwiched between two GaAsN strain-compensating layers (SCL) and AlGaAs cladding layers. By the aid of SCLs the photoluminescence (PL) wavelength red-shifted as much as 88 nm with the same intensity. GaInAsN strain-mediating layers (SML), having less strain than QW, were also used to obtain red shift and improved luminescence properties. The structures were studied by room temperature (RT) PL, x-ray diffraction (XRD) measurements and atomic force microscopy (AFM). The indium and nitrogen compositions of the QWs varied from 34 to 38 % and 1.3 to 3.5 %, respectively. Most of the studied structures showed PL peak wavelength at over 1.3 mm. Depending on the structure and thermal annealing treatment conditions the wavelength blue shifted up to 55 nm and intensity increased ~45 times. Furthermore, an AFM image of a five QW sample showed very smooth surface indicating together with PL measurements that high quality MQWs can be realized. In addition, 1.32-micrometers continuous-wave GaInAsN edge-emitting lasers were demonstrated.
We report on the growth of GaInNAs materials and lasers by molecular beam epitaxy (MBE) using a rf-plasma source. Optimal GaInNAs quantum well (QW) structures have been designed and grown in order to achieve the brightest and narrowest photoluminescence (PL) spectra beyond 1.30 um. State-of-the-art GaInNAs/GaAs SQW lasers operating at 1.32 um have been demonstrated. For a broad area oxide stripe, uncoated Fabry-Perot laser with a cavity length of 1600 um, the threshold current density is 546 A/cm2 at room temperature. Optical output up to 40 mW per facet under continuous wave operation was achieved for these uncoated lasers at room temperature.
Positron-annihilation measurements and nuclear reaction analysis (utilizing the 14N(d, p)15N and 14N(d, a)12C reactions) in conjunction with Rutherford backscattering spectrometry in the channeling geometry were used to study the defects in as-grown Ga(In)NAs materials grown by molecular beam epitaxy (MBE) using a radio-frequency (rf) plasma nitrogen source. Our data unambiguously show the existence of vacancy-type defects, which we attribute to Ga vacancies, and nitrogen interstitials in the as-grown Nitride-Arsenide epilayers. These point defects, we believe, are responsible for the low luminescence efficiency of as-grown Ga(In)NAs materials and the enhanced diffusion process during annealing.
We have reported for the first time on visible photoluminescence (PL) in crystallized a-Si:H/aSiNx:H multilayers structure by CW Ar ion laser annealing treatments. In this paper we present new results on visible PL and electroluminescence (EL) from crystallized a:SiH and its based multilayers by using KrF excimer pulse laser irradiating treatments. Strong and stable PL and EL have been observed by naked eye in both laser irradiated a-Si:H and a-Si:H/aSiNx:H multilayers samples at room temperature. The EL peak of crystallized a-Si:H/a-SiNx:H multilayers is blue shifted from 1.79 eV to 2.00 eV with narrowing the well layer thickness from 4 nm to 2 nm which suggests the origin of the light emission should be related to the quantum size effect.