Thomas Frost

Monolithic Electrically Injected Nanowire Array Edge-Emitting Laser on (001) Silicon

A silicon-based laser, preferably electrically pumped, has long been a scientific and engineering goal. We demonstrate here, for the first time, an edge-emitting InGaN/GaN disk-in-nanowire array electrically pumped laser emitting in the green (λ = 533 nm) on (001) silicon substrate. The devices display excellent dc and dynamic characteristics with values of threshold current density, differential gain, T0 and small signal modulation bandwidth equal to 1.76 kA/cm(2), 3 × 10(-17) cm(2), 232 K, and 5.8 GHz respectively under continuous wave operation. Preliminary reliability measurements indicate a lifetime of 7000 h. The emission wavelength can be tuned by varying the alloy composition in the quantum disks. The monolithic nanowire laser on (001)Si can therefore address wide-ranging applications such as solid state lighting, displays, plastic fiber communication, medical diagnostics, and silicon photonics.

Electrically pumped single-photon emission at room temperature from a single InGaN/GaN quantum dot

We demonstrate a semiconductor quantum dot based electrically pumped single-photon source operating at room temperature. Single photons emitted in the red spectral range from single In0.4Ga0.6N/GaN quantum dots exhibit a second-order correlation value g(2)(0) of 0.29, and fast recombination lifetime ∼1.3 ±0.3 ns at room temperature. The single-photon source can be driven at an excitation repetition rate of 200 MHz.

InGaN/GaN Quantum Dot Red

Lasers emitting in the 600 nm wavelength range have gained attention for a number of important applications, including optical information processing, plastic fiber communication systems, optical storage, and full color (RGB) laser displays and laser projectors. Visible lasers are currently realized with GaN-based heterostructures having InGaN/GaN quantum wells as the gain media. The performance of these devices, particularly at longer wavelengths, is limited by materials inhomogeneity and effects related to a large strain-induced polarization in the quantum wells. A laser emitting in the red (λ ~ 630 nm) has not been realized. Here, we demonstrate lasers which emit at 630 nm, the longest wavelength achieved with the nitride system, by incorporating InGaN/GaN self-organized quantum dots as the gain media. Strain relaxation during dot formation results in reduced polarization fields and consequently low threshold current density, Jth=2.5 kA/cm2, small blue shift of the emission peak, very weak temperature dependenc eof Jth (T0=236 K), and linearly TE polarized output.

(\lambda=630~{\rm nm})

InGaN/GaN disk-in-nanowire heterostructures on silicon substrates have emerged as important gain media for the realization of visible light sources. The nature of quantum confinement in the disks is largely unknown. From the unique nature of the measured temperature dependence of the radiative lifetime and direct transmission electron microscopy, it is evident that such self-organized islands (disks) behave as quantum dots. This is confirmed by the observation of single photon emission from a single disk-in-nanowire and the presence of a sharp minimum in the line width enhancement factor of edge emitting lasers having the InGaN disks as the gain media.

Laser

The characteristics of 1.55 μm InAs self-organized quantum-dot lasers, grown on (001) InP substrates by molecular beam epitaxy, have been investigated. Modulation doping of the dots with holes and tunnel injection of electrons have been incorporated in the design of the active (gain) region of the laser heterostructure. Large values of To=227 K (5^°C ≤ T ≤ 45^°C) and 100 K were derived from temperature dependent measurements of the light-current characteristics. The modal gain per dot layer is 14.5 cm^-1 and the differential gain derived from both light-current and small-signal modulation measurements is ~ 0.8×10^-15 cm². The maximum measured -3 dB small-signal modulation bandwidth is 14.4 GHz and the gain compression factor is 5.4×10^-17 cm². The lasers are characterized by a chirp of 0.6 Å for a modulation frequency of 10 GHz and a near zero α-parameter at the peak of the laser emission. These characteristics are amongst the best from any 1.55 μm edge-emitting semiconductor laser.

Formation and Nature of InGaN Quantum Dots in GaN Nanowires

The differential gain and coherent output characteristics of blue-emitting In0.18Ga0.82N/GaN quantum dot ridge waveguide lasers have been measured. The laser heterostructures were grown by molecular beam epitaxy. Injected carrier lifetimes in the quantum dots have been measured by temperature dependent and time resolved photoluminescence measurements. The radiative lifetime at 280 K is 480 ps. The threshold current densities at room temperature are 930 and 970 A/cm2 for pulsed and continuous wave bias operation, respectively. The measured differential gain is 2 × 10−16 cm2. The output slope and wall plug efficiency at 1050 A/cm2 under continuous wave operation are 0.4 W/A and 0.4%, respectively. The measured blue shift in the emission wavelength due to screening of the piezoelectric field with injection is as small as 4.4 nm.

High Performance InAs/

The small signal modulation characteristics of an InGaN/GaN nanowire array edge- emitting laser on (001) silicon are reported. The emission wavelength is 610 nm. Lattice matched InAlN cladding layers were incorporated in the laser heterostructure for better mode confinement. The suitability of the nanowire lasers for use in plastic fiber communication systems with direct modulation is demonstrated through their modulation bandwidth of f-3dB,max = 3.1 GHz, very low values of chirp (0.8 A) and α-parameter, and large differential gain (3.1 × 10−17 cm2).

{\rm In}_{0.53}{\rm Ga}_{0.23}{\rm Al}_{0.24}{\rm As}

We present a detailed study of the effects of dangling bond passivation and the comparison of different sulfide passivation processes on the properties of InGaN/GaN quantum-disk (Qdisk)-in-nanowire based light emitting diodes (NW-LEDs). Our results demonstrated the first organic sulfide passivation process for nitride nanowires (NWs). The results from Raman spectroscopy, photoluminescence (PL) measurements, and X-ray photoelectron spectroscopy (XPS) showed that octadecylthiol (ODT) effectively passivated the surface states, and altered the surface dynamic charge, and thereby recovered the band-edge emission. The effectiveness of the process with passivation duration was also studied. Moreover, we also compared the electro-optical performance of NW-LEDs emitting at green wavelength before and after ODT passivation. We have shown that the Shockley-Read-Hall (SRH) non-radiative recombination of NW-LEDs can be greatly reduced after passivation by ODT, which led to a much faster increasing trend of quantum efficiency and higher peak efficiency. Our results highlighted the possibility of employing this technique to further design and produce high performance NW-LEDs and NW-lasers.

/InP Quantum Dot 1.55

The measured characteristics of excited state lasing in tunnel injection p-doped InAs quantum dot lasers are reported. Excited state lasing at 1.22 μm is ensured by a high-reflectivity facet coating which is designed to suppress ground state lasing in the devices. The saturation modal gain in the excited states is 56 cm−1, which is a factor of ∼2.5 higher than that of the ground state. The small-signal modulation bandwidth for I=4.5Ith is 13.5 GHz and the differential gain is 1.1×10−15 cm2.

\mu{\rm m}

We report small-signal modulation bandwidth and differential gain measurements of a ridge waveguide In0.4Ga0.6N/GaN quantum dot laser grown by molecular beam epitaxy. The laser peak emission is at λ = 630 nm. The −3 dB bandwidth of an 800 μm long device was measured to be 2.4 GHz at 250 mA under pulsed biasing, demonstrating the possibility of high-speed operation of these devices. The differential gain was measured to be 5.3 × 10−17 cm2, and a gain compression factor of 2.87 × 10−17 cm3 is also derived from the small-signal modulation response.