Very low threshold InGaAsP mesa laser

Very low threshold currents InGaAsP/InP terrace mesa (T-ME) lasers with an unpassivated surface have been fabricated on semi-insulating (SI) InP substrates. Fabrication of the lasers involves a single-step liquid phase epitaxial (LPE) growth and a simple etching process. Lasers operating in the fundamental transverse mode with threshold currents as low as 6.3 mA (for a cavity length of 250 μm) have been obtained. Comparison between the unpassivated lasers and those passivated using the mass transport technique is described.     

Temperature dependence of the threshold current density of aquantum dot laser

Detailed theoretical analysis of the temperature dependence of threshold current density of a semiconductor quantum dot (QD) laser is given. Temperature dependences of the threshold current density components associated with the radiative recombination in QDs and in the optical confinement layer (OCL) are calculated. Violation of the charge neutrality in QDs is shown to give rise to the slight temperature dependence of the current density component associated with the recombination in QD's. The temperature is calculated (as a function of the parameters of the structure) at which the components of threshold current density become equal to each other. Temperature dependences of the optimum surface density of QD's and the optimum thickness of the OCL, minimizing the threshold current density, are obtained. The characteristic temperature of QD laser T_o is calculated for the first time considering carrier recombination in the OCL (barrier regions) and violation of the charge neutrality in QDs. The inclusion of violation of the charge neutrality is shown to be critical for the correct calculation of T_o. The characteristic temperature is shown to fall off profoundly with increasing temperature. A drastic decrease in T_o is shown to occur in passing from temperature conditions wherein the threshold current density is controlled by radiative recombination in QD's to temperature conditions wherein the threshold current density is controlled by radiative recombination in the OCL. The dependences of T_o on the root mean square of relative QD size fluctuations, total losses, and surface density of QDs are obtained     

Low threshold InGaAsP/InP buried crescent laser with double current confinement structure

An InGaAsP/InP laser diode emitting at 1.3 μm with a crescent shaped active region is described. The active region is completely embedded in InP by a two-step LPE technique, and a double current confinement scheme is incorporated with two reverse biased p-n junctions at both sides of the active layer. A threshold current as low as 20 mA has been achieved in CW operation at room temperature. Fundamental transverse mode operation with linear light output-current characteristics and single longitudinal mode oscillation have been obtained.     

Temperature dependence of threshold current for a quantum-well heterostructure laser

The threshold current density, J_th, of a quantum-well laser diode is calculated taking into account the quasi-two-dimensional nature of the heterostructure. The calculated value of J_th(T) for a quantum-well laser diode is found, in agreement with experiment, to be less temperature sensitive than that of a conventional double heterojunction laser. The step-like densities of states and the perturbed (hot) carrier distribution of a quasi-two-dimensional structure are responsible for the weaker temperature dependence. Supporting data on quantum-well Al_xGa_1-xAsGaAs heterostructure laser diodes grown by MO-CVD are presented showing that in the conventional expression J_th(T) = J_th(0) exp (T/T₀), T₀ can be as high as ～ 437°C.     

Temperature dependence of InGaAsP double-heterostructure laser characteristics

We report the temperature dependence of threshold for InGaAsP d.h. lasers with wavelengths from 1.23 to 1.53 ?m. Our results suggest that a recombination centre, rather than carrier leakage, is responsible for the temperature sensitivity of the thresholds.     

InGaAsP planar buried heterostructure laser diode (PBH-LD) with very low threshold current

Using a new LPE growth technique, an InGaAsP/InP planar buried heterostructure laser diode (PBH-LD) has been realised in 1.3 and 1.5 ?m wavelength regions. As a result of the effective carrier confinement, CW threshold currents as low as 8.5 mA and 13 mA have been obtained in 1.3 and 1.5 ?m PHB-LDs, respectively, at room temperature.     

The temperature dependence of the threshold current of GaInAsP/InP DH lasers

The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current Ithcalculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.     

Reflectivity dependence of threshold current in GaInAsP/InP surface emitting laser

A systematic study of changing the reflectivity of a Si/SiO/sub 2/ mirror for 1.3- mu m GaInAsP/InP surface-emitting lasers is discussed. An effective threshold current of 4.5 mA at 77 K continuous operation has been obtained. This indicates a possibility of a submilliampere threshold at 77 K and approximately=20 mA at 300 K by optimizing the mirror reflectivity.<>     

Auger recombination effect on threshold current of InGaAsP quantum well lasers

The Auger recombination effect on the threshold current of the InGaAsP quantum well (QW) laser is studied theoretically. All possible transitions between the quantized subbands of two-dimensional carriers are taken into account in evaluating the radiative process with thek-selection rule and the Auger process. The calculated threshold current agrees well with the reported experimental results for 1.07 μm InGaAsP QW lasers. The Auger component of the threshold current and its temperature dependence strongly depend on the QW structure, resulting in the necessity for an elaborate QW structure design, although both cannot be optimized at the same time. A design procedure is elucidated for a structure which gives the lowest threshold current density for the 1.07, 1.3, and 1.55 μm InGaAsP QW lasers.     

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T ³ in the case of Auger recombination.     

Surface roughness dependence of laser induced damage threshold

A functional relation between the rms roughness of a rough surface and the laser induced damage threshold is found. In deriving this relation it is assumed that the effective exposed area of the rough surface plays a dominant role in the damage mechanism. It is shown that the existing emperical relation between the rms roughness of a rough surface and the surface damage threshold could be derived from this functional relation under certain conditions.     

Temperature dependence of the threshold current for InGaAlP visiblelaser diodes

The temperature dependence of the threshold current for InGaAlP visible-light laser diodes was investigated from the standpoint of gain-current characteristics. The dependence of the light output power versus the current characteristic on the cavity length was evaluated for a 40-μm-wide InGaP-InGaAlP broad-stripe laser in the temperature range between -70 and 90°C. The threshold-current density dependence on the cavity length shows that a linear-gain approximation is suitable for this system. A minimum threshold-current density of 860 A/cm² was achieved at room temperature with a cavity length of 1160 μm. The internal quantum efficiency decreased in the temperature range higher than -10°C, which affected the excess threshold-current increase and the decrease in the characteristic temperature at this temperature range     

Low threshold current operation of vapour-grown 650 nm-band InGaAsP/InGaP DH lasers

InGaAsP/InGaP double heterojunction lasers emitting in the 650 nm band have been fabricated on GaAs0.61P0.39 substrates by hydride vapour-phase epitaxy. By optimising growth conditions and device structure, a threshold current density as low as 5.6 kA/cm2 is obtained, and CW operation is achieved up to ?27° C.     

Analysis of threshold current density and optical gain in InGaAsP quantum well lasers

Single-mode and multimode quantum well (QW) laser diodes with emission wavelengths λ=1.0 and 1.58 μm, based on MOCVD-grown separate-confinement heterostructures, have been studied. An analysis of the threshold current density and optical gain is made on the basis of experimental dependences of the threshold current and differential quantum efficiency on the cavity length. The threshold current is decomposed into principal components in terms of model approximations taking into account the Auger recombination, ejection of electrons from QWs into waveguide layers, and lateral current spreading to passive regions of a mesa-stripe laser. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 3, 2002, pp. 364–374. Original Russian Text Copyright ? 2002 by Pikhtin, Sliptchenko, Sokolova, Tarasov.     

Very low threshold current density room temperature continuous-wavelasing from a single-layer InAs quantum-dot laser

Continuous-wave (CW) lasing operation with a very low threshold current density (J_th=32.5 A/cm²) has been achieved at room temperature by a ridge waveguide quantum-dot (QD) laser containing a single InAs QD layer embedded within a strained InGaAs quantum well (dot-in-well, or DWELL structure). Lasing proceeds via the QD ground state with an emission wavelength of 1.25 μm when the cavity length is longer than 4.2 mm. For a 5-mm long QD laser, CW lasing has been achieved at temperatures as high as 40°C, with a characteristic temperature T₀ of 41 K near room temperature. Lasers with a 20 μm stripe width have a differential slope efficiency of 32% and peak output power of >10 mW per facet (uncoated)     

Length dependence of threshold current in multiple quantum welllasers

The threshold current density of single-quantum-well lasers increases at short laser lengths more rapidly than for multiple-well lasers. Using microscopic gain calculations, these differences are shown to be a natural consequence of the nonlinear gain/current relation associated with high electron concentrations in thin wells. The threshold current shows a minimum that depends on facet reflectivities and number of wells     

Fundamental characteristics of an InGaAsP/InP laser transistor

We have demonstrated a novel heterostructure device with functions of both a semiconductor laser and a heterojunction bipolar transistor, which is applicable to highly multifunctional optoelectronic integrated circuits. It can control both lasing power and output current. CW operation of the InGaAsP/InP transverse current injection laser at around room temperature has been achieved for the first time.     

Analysis of temperature dependence of CMOS transistors' threshold voltage

In this paper an investigation of influence of the metal-semiconductor work function difference on the threshold voltage of high-temperature (up to 473 K) operating CMOS transistors, which is often neglected in the literature, is presented. Expressions for temperature dependence of the threshold voltage of both Al-gate and Si-gate CMOS transistors, which take into account the influence of the metal-semiconductor work function difference, are derived starting from the standard expression for the MOS transistor threshold voltage. The temperature coefficient of the threshold voltage is considered in more detail, to provide a simple approximate model for the temperature dependence of the threshold voltage. It is shown that neglecting the temperature dependence of the metal-semiconductor work function difference significantly affects accuracy in prediction of the threshold voltage temperature behavior.     

The temperature dependence of threshold voltages in submicrometer CMOS

The temperature coefficient of the threshold voltage in long buried-p-channel MOSFET isdV_{th}/dT = 2.02mV/°C, which is much larger than that in the long enhancement-mode n-channel MOSFET (-1.27 mV/°C). The difference is caused by the charge freeze-out phenomenon in the buried-channel MOSFET. The absolute value of the temperature coefficient of the threshold voltage|dV_{th}/dT|, decreases with decreasing channel length in the n-channel MOSFET, however, it increases with decreasing channel length in the submicrometer p-channel MOSFET. The difference results from the majority-carrier spill-over phenomenon in the buried-p-channel MOSFET.     

Temperature dependence of threshold current of GaAs quantum well lasers

The radiative recombination rate in a quantum well structure is calculated using a constant density of states and the k-selection rule. This calculation shows that the threshold current of a GaAs quantum well laser has low temperature sensitivity (T0 ? 330 K for T > 300 K).