650 nm GalnP/AlGaInP laser diodes with low threshold and compressively strained MQW active layer

650 nm AIGalnP/GalnP laser diodes with compressively strained MQW active layer have been successfully fabricated by means of single epitaxy growth. The threshold current is 6.4 mA,at 40 mA CW operation, the fundamental transverse-mode still remains, and the output power and the slope efficiency can reach 34 mW and 1.1 mW/mA respectively. The dead output power in CW operation can reach 66 mW at a saturation current of 88 mA. During 200 h burn in test,the laser diodes show good stabilization with a degradation of less than 8 %.     

Thermal behavior of visible AlGaInP-GaInP ridge laser diodes

The thermal behavior of visible AlGaInP-GaInP ridge laser diodes was investigated numerically and experimentally. It is shown that various parameters critically influence the thermal resistance, R , of such devices. R is inversely proportional to the thermal conductivity of the heat sink. A substantial improvement in R is achieved for junction-side-down mounting compared to junction-side-up. R depends strongly on the width, w, of the ridge, and this effect is different for junction-side-up or junction-side-down mounting. In the first case, R~log(w) and in the second, R~1/w. The thickness of the soldering material is a sensitive parameter which may increase the value of R by up to 15 K/W. For junction-side-up mounted devices, the top metallization layer has a very favorable effect: a 1-μm-thick gold layer reduces R by 30%. It is shown that when a laser is switched on, the thermal steady state is reached in the millisecond time range. The experimental results show very good agreement with numerical data     

Impurity-free intermixing in compressively strained InGaAsP multiple quantum well structures

We report on controlled band gap modification in a compressively strained InGaAsP multi-quantum well-laser structure using different encapsulating layers followed by rapid thermal processing (RTP). The structure used was designed as a 1.55 μm laser with an active region consisting of three In_0.76Ga_0.24As_0.85P_0.15 quantum wells with In_0.76Ga_0.24As_0.52P_0.48 barriers grown by metal organic chemical vapor deposition. The heterostructure is capped with 100 nm thick InGaAs layer. Prior to RTP, the samples were coated with various dielectric layers or a thin film of low temperature (300°C) grown InP. Using a Si_xN_y film deposited by plasma-enhanced chemical vapor deposition with a refractive index of about 2.0, quantum well intermixing (QWI) was effectively suppressed. The suppression effect was independent of the Si_xN_y film thickness for layers of 30–2400 nm. With an e-beam-evaporated SiO₂ film, QWI was enhanced and a net blue shift of about 100 nm can be achieved between the samples covered with SiO₂ and Si_xN_y after RTP at 750°C for 100 s. Furthermore, InP grown at a low temperature by gas-source molecular beam epitaxy was proved to be even more efficient in enhancing QWI. Group V interstitial diffusion is used to explain the enhanced QWI between the wells and adjacent barriers which have the same group III compositions. Two-section tunable laser operated around 1.55 μm based on this laser structure was fabricated using this technique.     

Examination of intervalence band absorption and its reduction bystrain in 1.55 μm compressively strained InGaAs/InP laser diodes

Reduction of intervalence band absorption found in highly strained semiconductor lasers is dominated by enhancement in the TE gain spectrum due to the inclusion of compressive strain in the active layer and not by a change in the S-like character of the spin-orbit band     

Spontaneous emission efficiency of compressively strained 1.5 mu m MQW lasers

The spontaneous emission efficiency of 1.5 mu m compressively strained MQW lasers was found to be higher than that of comparable unstrained devices. The activation energy for Auger recombination was higher in the strained devices. Both effects were explained in terms of a reduction in the hole mass by strain.<>     

Steady-state and transient characteristics of microcavitysurface-emitting lasers with compressively strained quantum-well activeregions

In conventional semiconductor lasers, the dimensions of the optical cavity greatly exceed the photon wavelength, and the photon density of states forms a continuum since it is essentially that of a bulk system. On the other hand, in an ideal laser, one would like to have a single optical mode coincident with the maximum in the gain spectrum of the active medium. We show that substantial density-of-states quantization and enhancement of the fraction of photons spontaneously emitted into the lasing mode can be obtained by reducing the lateral width of the surface-emitting laser. For emission at λ=0.954 μm, the threshold current density can be drastically reduced by increasing the coupling factor to a few percent. For a cavity structure width of 0.3 μm, the threshold current density is 50 A/cm², compared with 250 A/cm² for the 0.6-μm cavity. At lower still lateral widths, the cavity loses its vertical character, and confinement of the lateral optical mode rapidly deteriorates. The large-signal response of microcavity lasers is slightly improved primarily due to elimination of mode competition in intrinsically single-mode microcavities, with relaxation times close to 1 ns. The enhancement of the spontaneous emission coupling factor results in an increase of the relaxation oscillation frequency and improvement in the standard small-signal response of microcavity lasers. For J=10J_th, the -3 dB modulation frequency exceeds 40 GHz. Since low threshold current densities may be achieved in microcavity lasers, the gains in small-signal performance are primarily extrinsic, i.e., higher modulation bandwidths ace accessible for the same injection     

1.5 μm multiquantum-well semiconductor optical amplifier withtensile and compressively strained wells for polarization-independentgain

A multiquantum-well optical amplifier for 1.5-μm wavelength operation using alternating tensile and compressively strained wells in the active region is described. For each bias level measured, the polarization sensitivity of the amplifier gain is 1 dB or less averaged over the gain bandwidth. This amplifier is suitable for integration with other optical devices in photonic integrated circuits which require polarization-independent gain     

High-speed 1.5-μm compressively strained multi-quantum wellself-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5-μm MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9×10 ^-12 m³/s. The estimated intrinsic maximum bandwidth is 68 GHz     

White-light emission from InGaN-GaN multiquantum-welllight-emitting diodes with Si and Zn codoped active well layer

Si and Zn codoped In_xGa_1-xN-GaN multiple-quantum-well (MQW) light-emitting diode (LED) structures were grown by metal-organic vapor phase epitaxy (MOVPE). It was found that we can observe a broad long-wavelength donor-acceptor (D-A) pair related emission at 500 nm~560 nm. White light can thus be achieved by the combination of such a long-wavelength D-A pair emission with the InGaN bandedge related blue emission. It was also found that the electroluminescence (EL) spectra of such Si and Zn codoped InGaN-GaN MQW LEDs are very similar to those measured from phosphor-converted white LEDs. That is, we can achieve white light emission without the use of phosphor by properly adjusting the indium composition and the concentrations of the codoped Si and Zn atoms in the active well layers and the amount of injection current     

Anomalous in-plane polarization dependence of optical gain in compressively strained GaInAsP-InP quantum-wire lasers

In-plane polarization anisotropy of optical gain in compressively strained GaInAsP-InP quantum wire (Q-wire) lasers including elastic strain relaxation induced band mixing is studied. The interaction between two-dimensional (2-D) quantum confinement and elastic strain relaxation effects is found to be complex depending qualitatively also on the wire width. Additional valence band mixing due to strain relaxation has a strong influence on the polarization dependence of optical gain. In the absence of elastic strain relaxation, gain is the maximum for tranverse electric (TE) polarization with the electric field parallel to the wire axis (TE/sub /spl par//), in agreement with the existing theory. On the other hand, when strain relaxation is strong, contrary to the existing theory, valence band mixing causes the gain to be the maximum in TE polarization with the electric field normal to the wire axis (TE/sub /spl perp//). Moreover, Q-wire lasers without suppression of strain relaxation are more likely to exhibit ground-state lasing for TE/sub /spl perp// polarization. These results suggest that in the presence of strong strain relaxation, a laser cavity parallel to the wire axis would provide higher gain. Therefore, the appropriate orientation of the laser cavity in strained GaInAsP-InP Q-wire lasers should be decided after carefully studying the polarization dependence of gain. Our calculation also shows that strong strain relaxation causes in-plane polarization anisotropy to show complex, nonmonotonic dependence on the wire width. Consequently, in such structures, in-plane polarization anisotropy may not be regarded as a direct measure of 2-D confinement effects.     

Theoretical threshold lowering of compressively strained InGaAs/InGaAsP and GaInAsP/GaInAsP quantum-well lasers

The first theoretical evaluation is reported of the effect of biaxial compression on the quantum-well Ga/sub x/In/sub 1-x/As/Ga/sub 0.20/InAs/sub 0.45/P and Ga/sub 0.20/In/sub 0.80/As/sub y/P/sub 1-y//Ga/sub 0.20/In/sub 0.80/As/sub 0/ /sub .45/P/sub 0.55/ laser threshold current density. Reference is made to known experimental results, and a comparison carried out of the potentialities of the two types of laser.<>     

The energy-limiting characteristics of a polarization-maintaining Sagnac interferometer with an intraloop compressively strained quantum-well saturable absorber

An experimental demonstration of an energy limiter for short pulses at 1550 nm is reported. The limiter is based on an optical fiber Sagnac loop with an intraloop dichroic saturable absorber based on an InGaAsP-based waveguide with compressively strained multiple quantum wells. The saturable absorber is placed asymmetrically in the loop and is used as a Kerr-like nonlinear phase shifter. The device is operated in a novel dual polarization scheme, which offers some unique advantages. Excellent limiting for noise reduction purposes is demonstrated with the device.     

Characteristics dependence on confinement structure and single-modeoperation in 2-μm compressively strained InGaAs-lnGaAsP quantum-welllasers

The optimum confinement layer structure in 2-μm compressively strained InGaAs-InGaAsP lasers is experimentally studied. Beside the carrier overflow and absorption loss in the confinement layers, the intervalence band absorption and/or Auger recombination play an important role in laser characteristics. More attention should be paid to the confinement structure to reduce the carrier density. We obtained a better laser performance with an energy difference between the bandgap of the optical confinement layer and the laser transition energy of 280-300 meV. A distributed-feedback (DFB) laser operating at 2.043 μm has been realized with the threshold current as low as 6 mA and the maximum output power of 6 mW. The differential quantum efficiency and the characteristic temperature are 16% and 59 K, respectively     

Dependence of the linewidth enhancement factor on the number of compressively strained quantum well in lasers

We have systematically studied the well number dependence of the linewidth enhancement factor in strained quantum-well (QW) lasers and have demonstrated experimentally that the linewidth enhancement factor can be reduced from /spl sim/9.4 to /spl sim/2.0 by increasing the number of compressively strained QW's from 2 to 8. This behavior is primarily due to an increase in the differential gain with the number of QW's.     

Stability of polymer light-emitting diodes

In this paper, we report on the lifetime of polymer LEDs fabricated at Philips Research. For single-layer LEDS, we find that the operational lifetime in nitrogen gas is limited by the stability of the indium-tin-oxide (ITO) anode. By using a polymeric capping layer for the ITO, we obtain more stable devices. In air, the lifetime is limited by black spot formation. Small pinholes in the cathode layer are the origins of the black spots. Water or oxygen may diffuse through these pinholes and react with the cathode, causing degradation. By encapsulating the devices we can prevent black spot formation. Our present 8 cm² devices have lifetimes of many thousands of hours at daylight visibility under ambient conditions.     

All-selective MOVPE-grown 1.3-μm strained multi-quantum-wellburied-heterostructure laser diodes

Strained InGaAsP multi-quantum-well (MQW) double-channel planar-buried-hetero (DC-PBH) laser diodes (LDs) were fabricated by selective metalorganic-vapor-phase epitaxy (MOVPE). In the laser fabrication process, both the strained MQW active layer and current blocking structure were directly formed by selective MOVPE without any semiconductor etching process. The LDs are called all-selective MOVPE-grown BH LDs. The laser fabrication process can achieve both a precisely controlled gain waveguide structure and an excellent current blocking configuration, realizing the optimized DC-PBH structure. These aspects are essential to the high-performance and low-cost LD, which is strongly demanded for optical access network systems or fiber-to-the-home networks. This paper will show the excellent high-temperature characteristics for 1.3-μm Fabry-Perot LDs which have a record threshold current of 18 mA with a low-operation current of 56 mA for 10 mW, and 74 mA for 15 mW at 100°C with extremely high uniformity. Furthermore, reliable long-term operation at high temperature (85°C) and high-output power of 15 mW has been demonstrated for the first time     

Wideband and high-power compressively strained GaInAsP/InPmultiple-quantum-well ridge waveguide lasers emitting at 1.3 μm

Compressively strained 1.3-μm GaInAsP/InP multiple-quantum-well (MQW) ridge waveguide lasers were fabricated. Through optimizing the total well thickness, large bandwidth over 11 GHz was achieved, together with high quantum efficiency of about 0.48 W/A and high power output of 60 mW before rollover. The laser also showed less temperature sensitivity up to an elevated temperature of 85°C     

Experimental study of Auger recombination, gain, and temperaturesensitivity of 1.5 μm compressively strained semiconductorlasers

The effect of strain on Auger recombination has been studied using the differential carrier lifetime technique in both lattice matched InGaAs-InP and compressively strained quaternary quantum wells. It is found that Auger recombination is reduced in strained devices. The transparency carrier density and differential gain of both lattice matched and strained devices have been obtained by gain and relative intensity noise measurement. A reduction of the transparency carrier density is observed in the strained device. However, no differential gain increase is seen. The temperature sensitivity of the threshold current density of both lattice matched and strained devices has been fully studied. Physical parameters contributing to the temperature sensitivity of the threshold current density have been separately measured, and it is shown that the change in differential gain with temperature is a dominant factor in determining the temperature sensitivity of both lattice matched and strained devices     

Photovoltaic-p-i-n diodes for RF control-switching application

A photovoltaic-p-i-n diode switch, consisting of two back-to-back p-i-n diodes which can be forward biased to the ON state by photovoltaic cell photocurrents, is introduced for optically controlling RF signals. Without light, the switch is in the OFF state and isolation is determined by the diode junction capacitance. We report a device operating in the VHF range and handling 25 W. With 40 mA photocurrent injected into each diode, the measured insertion loss at 25-W input power is ≈0.08 dB, mainly limited by the diode series resistance; its capacitance was 380 fF. Experiments indicate that low insertion loss requires the signal period ≪ carrier lifetime so that carrier sweep out in the I-region does not reduce conductivity