Self-assembled indium arsenide quantum-dash lasers on indium phosphide substrates

A new type of low-dimensional nanostructure—the self-assembled InAs quantum dash—is grown in a strained AlGaInAs quantum well and employed as the active region of lasers on InP substrates with (001) orientation. The quantum dashes are essentially quantum dots, but are elongated along one direction (along [11¯0] in this case). The work presented in this dissertation on the growth and characterization of 1.55 μm range InAs quantum-dash lasers demonstrates the unique properties of these devices.; Characteristics of single-, three-, and five-stack InAs quantum-dash lasers were investigated using a broad-area device structure. Pulsed room temperature operation demonstrates wavelengths from 1.60–1.66 μm, a threshold current density as low as 350 A/cm2, and a distinctly quantum wire-like dependence of the threshold current on the laser cavity orientation. The maximal modal gain for lasing in the ground-state is determined to be 15 cm−1 for single-stack lasers, which is double that of comparable quantum-dot lasers. These self-assembled InAs quantum-dash lasers with emission wavelengths in the new optical fiber L-band and reasonable low thresholds are very promising for wavelength-division-multiplexing (WDM) applications.; A novel processing technology—oxidized ridge waveguide—was developed for InP-based lasers. Five-μm ridges are formed by induced coupled plasma (ICP) etching and wet oxidation to convert p-Al_0.48In _0.52As into Al(In)O_x serving as a current-blocking layer. A comparison between this oxidized-ridge-waveguide laser and a conventional ridge waveguide laser is made to show that a 30% higher efficiency and a 30% lower threshold current density are achieved by using this new fabrication method. Electroluminescense (EL) spectrum from an oxide-confined LED shows clearly quantum dot-like discrete energy levels and low energy state saturation. Due to this property, quantum-dash lasers are very desirable to serve as gain chips for tunable lasers.; A 123 nm tuning range from 1.484 μm to 1.607 μm is obtained under cw operation at 15°C by using an external-cavity tunable laser (ECL) with Littrow configuration. The gain chip is a 5-stack quantum-dash oxidized-ridge-waveguide laser with 2.5 mm cavity length and broadband AR-coating (0.15% reflectivity) on one facet. The threshold current density is below 1.1 kA/cm2 for all the tuning wavelengths. This ECL with tunability nearly covering the very important S-, C-, and L-band of Er-doped fiber amplifiers and relatively low threshold is desirable for a dense-wavelength-division-multiplexing (DWDM) tunable light source.; Finally, the transition matrix element theory was used to calculate the ratio of the width to the height of the quantum dash.