Lasing emission of InGaAs quantum dot microdisk diodes

An improved three-arm airbridge contacted microdisk diode structure is presented. Continuous-wave lasing from InGaAs quantum dot (QD) in a /spl sim/4-/spl mu/m-diameter microdisks is reported with the threshold current /spl sim/40 /spl mu/A at T=5 K. With the increase of injection current, the QD's emission blueshifts due to the band-filling effect, while the laser mode peak redshifts by thermal effect. When the QD's gain spectra shift out of alignment with the lasing mode, the next available whispering gallery mode starts lasing from QD wetting layer. The thermal heating effect is discussed by investigating the modes redshift with respect to injection current.     

Engineering laser gain spectrum using electronic vertically coupled InAs-GaAs quantum dots

Continuous large-broad laser gain spectra near 1.3 /spl mu/m are obtained using an active region of electronic vertically coupled (EVC) InAs-GaAs quantum dots (QDs). A wide continuous electroluminescence spectrum, unlike that from conventional uncoupled InAs QD lasers, was obtained around 230 nm (below threshold) with a narrow lasing spectrum. An internal differential quantum efficiency as high as 90%, a maximum measured external differential efficiency of 73% for a stripe-length of L=1 mm, and a threshold current density for zero total optical loss as low as 7 A/cm/sup 2/ per QD layer were achieved.     

High-frequency modulation characteristics of 1.3-/spl mu/m InGaAs quantum dot lasers

In this letter, we report results of small-signal modulation characteristics of self-assembled 1.3-/spl mu/m InGaAs-GaAs quantum dot (QD) lasers at room temperature. The narrow ridge-waveguide lasers were fabricated with multistack InGaAs self-assembled QDs in active region. A high characteristic temperature of T/sub o/=210 K with threshold current density of 200A/cm/sup 2/ was obtained. Small-signal modulation bandwidth of f/sub -3 dB/=12 GHz was measured at 300 K with differential gain of dg/dn/spl cong/2.4/spl times/10/sup -14/ cm/sup 2/ from detailed characteristics. We observed that a limitation of modulation bandwidth in high current injection appeared with gain saturation. This property can direct future high-speed QD laser design.     

High-modal gain 1300-nm In(Ga)As-GaAs quantum-dot lasers

A semiconductor laser containing seven InAs-InGaAs stacked quantum-dot (QD) layers was grown by molecular beam epitaxy. Shallow mesa ridge-waveguide lasers with stripe width of 120 /spl mu/m were fabricated and tested. A high modal gain of 41 cm/sup -1/ was obtained at room temperature corresponding to a modal gain of /spl sim/6 cm/sup -1/ per QD layer, which is very promising to enable the realization of 1.3-/spl mu/m ultrashort cavity devices such as vertical-cavity surface-emitting lasers. Ground state laser action was achieved for a 360-/spl mu/m-cavity length with as-cleaved facets. The transparency current density per QD layer and internal quantum efficiency were 13 A/cm/sup 2/ and 67%, respectively.     

Theory of pulse-train amplification without patterning effects in quantum-dot semiconductor optical amplifiers

A theory for pulse amplification and saturation in quantum dot (QD) semiconductor optical amplifiers (SOAs) is developed. In particular, the maximum bit rate at which a data stream of pulses can be amplified without significant patterning effects is investigated. Simple expressions are derived that clearly show the dependence of the maximum bit rate on material and device parameters. A comparative analysis of QD, quantum well (QW), and bulk SOAs shows that QD SOAs may have superior properties; calculations predict patterning-free amplification up to bit rates of /spl sim/150-200 Gb/s with pulse output energies of /spl sim/0.2-0.4 pJ. The superiority of QD SOAs is based on: 1) the faster achievement of the regime of maximum gain in QD SOAs compared to QW and bulk SOAs and 2) the lower effective cross section of photon-carrier interaction in QDs.     

Linewidth study of InAs-InGaAs quantum dot distributed feedback lasers

The linewidth of laterally loss-coupled distributed feedback (DFB) lasers based on InAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) is investigated. Narrow linewidth operation of QD devices is demonstrated. A linewidth-power product less than 1.2 MHz /spl middot/ mW is achieved in a device of 300-/spl mu/m cavity length for an output power up to 2 mW. Depending on the gain offset of the DFB modes from the QD ground state gain peak, linewidth rebroadening or a floor is observed at a cavity photon density of about 1.2-2.4/spl times/10/sup 15/ cm/sup -3/, which is much lower than in QW lasers. This phenomenon is attributed to the enhanced gain compression observed in QDs.     

1.3-/spl mu/m InAs quantum-dot laser with high dot density and high uniformity

We realized a triple-stacked 1.3-/spl mu/m InAs quantum dot (QD) with a high density of 2.4/spl times/10/sup 11/ cm/sup -2/ and a high uniformity of below 24 meV that employs an As/sub 2/ source and a gradient composition (GC) strain-reducing layer (SRL) grown on a GaAs substrate. We demonstrated the 1.3-/spl mu/m wavelength emission of this triple-stacked QD laser with a 0.92-mm cavity length and a cleaved facet at room temperature. In addition, we realized the highest maximum modal gain yet reported of 8.1 cm/sup -1/ per QD layer at beyond 1.28 /spl mu/m by using our high-density and high-uniformity QD.     

Temperature dependence of gain saturation in multilevel quantum dotlasers

The temperature dependence of quantum dot (QD) optical gain is analyzed using a multilevel model and compared with experiment. The maximum gain is found to have a surprisingly strong temperature dependence that causes level switching and can limit laser performance in QD lasers. The model based on multiple discrete levels elucidates general design criteria that should be satisfied to obtain a stable threshold versus temperature in QD lasers. Good agreement is obtained between calculations and experiment for level switching in 1.3-μm QD lasers     

The impact of energy band diagram and inhomogeneous broadening on the optical differential gain in nanostructure lasers

We present a general theoretical model for the optical differential gain in semiconductor lasers. The model describes self assembly quantum dots (QDs), self assembly quantum wires (QWRs) and single quantum-well lasers. We have introduced the inhomogeneous broadening due to size fluctuations in the assembly cases. At each dimensionality, we have considered the carrier populations in the excited states and in the reservoirs, where conduction and valence bands are treated separately. We show that for room temperature operation the differential gain reduction due to increased size inhomogeneity is more pronounced in QDs than in QWRs. We show this reduction to be smaller than the one-order reduction attributed to state filling in conventional dot and wire assemblies operating at room temperature. The integration prefactor coefficient of the differential gain in zero-dimensional cases exceed one- and two-dimensional coefficients only for low temperatures where the homogenous broadening is considerably smaller than the thermal energy. The differential gain of QDs, QWRs, and compressively strained single quantum-well lasers operating at room temperature and close to equilibrium is nearly the same.     

Electroluminescence from the Ge quantum dot MOS tunneling diodes

A Ge quantum dot (QD) light-emitting diode (LED) is demonstrated using a MOS tunneling structure for the first time. The oxide film was grown by liquid phase deposition at 50/spl deg/C to reduce the thermal budget. The infrared emission of /spl sim/1.5 /spl mu/m was observed from Ge QD MOS LEDs, similar to the p-type-intrinsic-n-type structure reported previously. At the negative gate bias, the electrons in the Al gate electrode tunnel to the Ge QD through the ultrathin oxide and recombine radiatively with holes to emit the /spl sim/1.5/spl mu/m infrared. The electrons also recombine with holes in the Si cap, and the band edge emission from Si is also observed.     

Measurement of modal gain in 1.1 /spl mu/m p-doped tunnel injection InGaAs/GaAs quantum dot laser heterostructures

Single-pass optical gain of self-assembled InGaAs/GaAs p-doped tunnel injection quantum dot laser heterostructures emitting at 1.1 /spl mu/m is measured by the multisection device technique. The heterostructures, consisting of three layers of quantum dots in the active region, demonstrate net modal gain as high as 57 cm/sup -1/.     

Room-temperature operation of InP-based InAs quantum dot laser

A ridge waveguide quantum dot (QD) laser with a stripe width of 15 /spl mu/m was fabricated by using the seven-stacked InAs QD layers based on the InAlGaAs-InAlAs material system on InP [001] substrate. Room-temperature lasing operation was observed at 1.501 /spl mu/m, which is the first observation from the InAs QDs with the InAlGaAs-InAlAs structure. The characteristic temperature of the InAs QD laser calculated from the temperature dependence of threshold current density was 135 K in the temperature range from 200 K to room temperature.     

Sensitivity of double-gate and FinFETDevices to process variations

We investigate the manufacturability of 20-nm double-gate and FinFET devices in integrated circuits by projecting process tolerances. Two important factors affecting the sensitivity of device electrical parameters to physical variations were quantitatively considered. The quantum effect was computed using the density gradient method and the sensitivity of threshold voltage to random dopant fluctuation was studied by Monte Carlo simulation. Our results show the 3/spl sigma/ value of V/sub T/ variation caused by discrete impurity fluctuation can be greater than 100%. Thus, engineering the work function of gate materials and maintaining a nearly intrinsic channel is more desirable. Based on a design with an intrinsic channel and ideal gate work function, we analyzed the sensitivity of device electrical parameters to several important physical fluctuations such as the variations in gate length, body thickness, and gate dielectric thickness. We found that quantum effects have great impact on the performance of devices. As a result, the device electrical behavior is sensitive to small variations of body thickness. The effect dominates over the effects produced by other physical fluctuations. To achieve a relative variation of electrical parameters comparable to present practice in industry, we face a challenge of fin width control (less than /spl sim/1 nm 3/spl sigma/ value of variation) for the 20-nm FinFET devices. The constraint of the gate length variation is about 10/spl sim/15%. We estimate a tolerance of 1/spl sim/2 /spl Aring/ 3/spl sigma/ value of oxide thickness variation and up to 30% front-back oxide thickness mismatch.     

1.3 /spl mu/m quantum dot vertical-cavity surface-emitting laser with external light injection

A 1.3 /spl mu/m quantum dot vertical-cavity surface-emitting laser (QD VCSEL) with external light injection is presented, having been experimentally demonstrated. The QD VCSEL is fabricated on GaAs substrate. The 3 dB frequency response of the QD VCSEL based on the TO-Can package is enhanced from the free-running 1.75 to 7.44 GHz with the light injection technique.     

InAs-InAlGaAs quantum dot DFB lasers based on InP [001]

The InAs-InAlGaAs quantum dot (QD) lasers with the InAlGaAs-InAlAs material system were fabricated on distributed feedback (DFB) grating structures on InP [001]. The single-mode operation of InAs-InAlGaAs QD DFB lasers in continuous-wave mode was successfully achieved at the emission wavelength of 1.564 /spl mu/m at room temperature. This is the first observation on the InP-based QD lasers operating around the emission wavelength window of 1.55 /spl mu/m. The threshold current density of the InAs-InAlGaAs QD DFB laser with a cavity length of 1 mm and a ridge width of 3 /spl mu/m, in which one of the cleaved facets was coated with 95% high-reflection, was 1.23 kA/cm/sup 2/ (176 A/cm/sup 2/ for single QD layer). The sidemode suppression ratio value of the QD DFB laser was as high as 42 dB at the driving current of 100 mA.     

Feasibility study for degenerate two-photon gain in a semiconductor microcavity

We analyze the magnitude of degenerate two-photon gain of several quantum wells (QWs) in a resonant microcavity which is pumped off-resonantly by an optical field. A set of coupled phenomenological rate equations for electron-hole pairs and photons is derived. In the framework of this model, we make a realistic prediction of the time-integrated two-photon gain and find that a /spl lambda/-cavity containing 11 QWs would give a maximal amplification of /spl sim/2.3% for a peak intensity of /spl sim/80 MW/cm/sup 2/. A better insight into the dependence of the gain on the various physical parameters is given by an analytical formula resulting from various approximations on the rate equations.     

Origin of size distributions in ZnSe self-organized quantum dots grown on ZnS layers

Main factors which determine the size, the standard deviations which show the degree of the size fluctuations for the average dot height and diameter, and density in ZnSe self-organized quantum dots (QDs) grown on ZnS layers were studied. By lowering the growth temperature the QDs average size and its standard deviation decreased and the density increased due to the slower surface migration. With the application of the scaling theory, it was revealed that the normalized size distributions were uniquely determined by the nucleation process although the apparent standard deviations of the QD sizes were dependent on the growth temperature. The influence of surface roughness of the underneath layer on the formation of the relations of the dot height and diameter was also examined. It was shown that the fluctuation of the surface potential contributes significantly to the apparent standard deviations of ZnSe self-organized QDs sizes.     

PbSe量子点掺杂玻璃的制备及表征

采用高温熔融法,经过两步热处理,成功制备了PbSe量子点(QD)掺杂的硅酸盐玻璃.当热处理温度为550℃、热处理时间为1～10 h时,X射线衍射(XRD)和透射电镜(TEM)测量表明,玻璃中,生成的PbSe QD平均尺寸为5～6 nm.随着热处理时间的延长(3～8 h),玻璃中生成的PbSe QD尺寸增大.近红外荧光(...     

10 Gbit/s data modulation using 1.3 /spl mu/m InGaAs quantum dot lasers

Error-free 8 and 10 Gbit/s data modulation with quantum dot lasers emitting at 1.3 /spl mu/m is presented. 12 Gbit/s open eye patterns are observed. An integrated fibre-optic QD laser module yields error-free data modulation at 10 Gbit/s at a receiver power of -2 dBm.     

Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.