InAsSb/InAsSbP double-heterostructure lasers emitting at 3–4 µm: Part I

Previous publications concerned with the development and investigation of InAsSb/InAsSbP double heterostructure lasers emitting at 3–4 μm fabricated by liquid phase epitaxy are reviewed. In pulsed mode, the maximum operating temperature of the lasers is 203 K, the characteristic temperature is 35 K, and differential quantum efficiency is 20±5% at 77K. Mesa-stripe lasers with a 10-to 30-μm stripe width and a 200-to 500-μm cavity length can operate in CW mode up to 110 K. The total optical output power of more than 10 mW at λ=3.6 μm is obtained at T=82 K in CW mode. The output power per mode does not exceed 2 mW/facet. A single-mode lasing is achieved in the temperature range of 12–90 K. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 11, 2000, pp. 1396–1403. Original Russian Text Copyright ? 2000 by Danilova, Imenkov, Sherstnev, Yakovlev.     

Mechanisms of radiative recombination in InGaAsSb/InAsSbP lasers operating in the 3.0 to 3.6-µm spectral range

It is shown that type-I or type-II heterojunctions can be formed at heterojunction boundaries, depending on the composition of the active region and/or bounding layers. This is governed by differences in the mechanisms of radiative recombination, the temperature dependence of the radiation wavelength, the polarization type of the radiation, and the current-voltage characteristics. Fiz. Tekh. Poluprovodn. 33, 233–238 (February 1999)     

Emission-line broadening of current tunable InAsSbP/InAsSb/InAsSbP heterostructure lasers

The dependence of emission-line broadening on the drive current was studied at 50–80 K for tunable InAsSbP/InAsSb/InAsSbP double heterostructure lasers operating in the 3.3–3.4 μm spectral region. For a small increase of the injection current I over the threshold current I _th, the line width depends on the I-I _th difference hyperbolically, in accordance with the Schawlow-Townes and Henry theories that assume a homogeneous distribution of the nonequilibrium carrier concentration across the resonator width. With the current raised to (3–4)I _th, line narrowing ceases and the line starts to broaden with increasing current. The observed line broadening is explained by the effect of the nonequilibrium carrier concentration gradient between the middle of the resonator and its edges. In tunable lasers, this gradient increases with current, the lasing wavelength simultaneously decreasing. The minimal width of the lasing line is 10–20 MHz. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 12, 2000, pp. 1468–1471. Original Russian Text Copyright ? 2000 by Imenkov, Kolchanova, Kubat, Civish, Yakovlev.     

High power InGaAsSb(Gd)/InAsSbP double heterostructure lasers (λ=3.3 µm)

InGaAsSb(Gd)/InAsSbP double heterostructure lasers (λ=3.3 μm, T=77 K) yield a multimode power of 1.56 W in pulsed operation (pulse width 30 μs, repetition frequency f=500 Hz) and 160 mW in the continuous-wave (CW) case. In the single-mode CW operation, the power is 18.7 mW. It is shown that heating of the active region is responsible for sublinear light-current characteristics in “long-cavity” lasers, whereas in “short-cavity” (L=140–300 μm) lasers the power is mainly limited by internal losses. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 10, 2001, pp. 1261–1265. Original Russian Text Copyright ? 2001 by Aydaraliev, Zotova, Karandashev, Matveev, Remennyi, Stus’, Talalakin.     

InAsSbP double-heterostructure lasers for the spectral range 2.7–3.0 µm (T=77 K)

We have produced, by using liquid-phase epitaxy, 2.7 to 3.0-μm lasers based on InAsSbP double-heterostructures with different phosphorus contents in the active and wide-gap regions. The lasers possess threshold current density ∼0.8 kA/cm² at 77 K and operate in the pulsed mode up to ∼124 K with maximum threshold current density 10–12 kA/cm². The lasers have a low series resistance ∼0.45 Ω. Fiz. Tekh. Poluprovodn. 32, 241–244 (February 1998)     

Spectral and mode characteristics of InAsSbP/InAsSb/InAsSbP lasers in the spectral region near 3.3 µm

The characteristic features of the continuous-wave lasing spectra near 3.3 μm of multimode InAsSbP/InAsSb/InAsSbP double-heterostructure diode lasers are shown. The observation of mode switching to longer and shorter wavelengths at cryogenic temperatures is reported. It is shown that suppression of the longitudinal side modes closest to the main mode results in large mode jumps in energy during mode tuning by current. The characteristics which were observed are explained by gain spectrum inhomogeneity due to spectral hole burning in narrow-gap semiconductors. The intraband charge-carrier relaxation times in the active region are estimated. Fiz. Tekh. Poluprovodn. 39, 1139–1144 (September 1998)     

AlGaAs/GaAs双异质结激光器退化的研究

观察了室温下工作的DH激光器退化现象,发现在短时间内退化的器件,除阈值升高外尚伴随着微分量子效率下降。对热稳定性良好,并对于较长时间(>250小时)阈值上升率(△J_(th)/J_(th)千小时)小于3％的器件,高温老化证明它们的寿命都能超过万小时量级。     

Spatial beam oscillations in stripe lasers utilizing InAsSb/InAsSbP heterojunctions

Anomalously narrow, single-lobe and double-lobe beam directivity patterns in the plane of the p-n junction have been observed in lasers constructed from InAsSb/InAsSbP heterojunctions emitting at a wavelength of approximately 3.3 μm. Theoretical near-field and far-field radiation distributions for the laser emission of two beams oscillating across the stripe are obtained on the basis of new concepts of the lasing processes. The single-lobe directivity pattern is obtained for the emission of in-phase beams, and the double lobe is obtained for antiphase beams. Correspondence of the theory with experiment is established. Fiz. Tekh. Poluprovodn. 33, 1014–1019 (August 1999)     

Zn-diffused, stripe-geometry, double-heterostructure GaInAsP/InP diode lasers

Deep Zn diffusion from a ZnP2source has been used to fabricate stripe-geometry double-heterostructure GaInAsP/InP diode lasers with emission wavelengths in the1.2-1.3 mum range. These devices exhibit good electrical and optical confinement. For sufficiently narrow stripe widths (<10 mum), emission is usually single mode and linear. CW outputs up to ∼8 mW per facet have been observed. In initial life tests, two Zn-diffused lasers have operated CW at room temperature for over 5000 h without appreciable degradation.     

Carrier-induced index change in AlGaAs double-heterostructure lasers

A large carrier-induced index change is reported for conventional 8 ?m-stripe oxide-isolated AlGaAs double-heterostructure lasers. At threshold, the index change of the active layer is ?0.05 to ?0.07, which is a factor of 5 to 10 larger than previously reported. It is accompanied by an even greater change in dispersion. These effects cannot be explained by a free-carrier effect, and are most likely caused by a carrier-induced shift of the absorption edge.     

Self-focusing effects in pulsating AlxGa1-xAs double-heterostructure lasers

Using proton bombarded stripe geometry lasers which emit intense optical pulses, we have measured the width of the optical beam in the plane of the junction as a function of time during the pulse. The width of the beam is qualitatively proportional to the change in the carrier density. The width increases during the quiescent period between pulses where the carrier density increases by current injection and decreases during the emission of the pulse. For one laser studied in considerable detail, the full width at half intensity decreases from 9 μm at the start of the pulse to 7.2 μm at the end of the pulse. The reduction in the width results from the self-focusing of the beam. It is due to an increase in the refractive index and the decrease in the gain distributions near the center of the stripe. The reduction in the beamwidth concentrates the mode to a region of sufficiently higher average gain to compensate for the reduction in spatial gain distribution. The self-focusing acts to reduce the damping of the relaxation oscillations, and thus enhances the effect of other nonlinearities such as saturable absorption in causing pulsations. The thermal induced refractive index distribution across the stripe is shown to play a crucial role in the gain instability caused by self-focusing.     

Molecular-beam epitaxially grown 1.3 ?m GaInAsP/InP double-heterostructure lasers

We report the first successful preparation of current-injection GaInAsP/InP double-heterostructure laser lasing at 1.3 ?m by molecular beam epitaxy. For broad-area Fabry-Perot diodes of 380 ?m×200 ?m and an active layer thickness of 0.2 ?m, we have observed threshold current densities Jth as low as 1.8 kA/cm2 and a median Jth?3.5 kA/cm2.     

Optical parameters of diode lasers based on an InAsSb/InAsSbP heterostructure

The rates of radiative recombination (including transitions induced by enhanced luminescence) and nonradiative recombination, internal quantum yield of luminescence, and the matrix element for band-to-band optical transitions were determined for the first time for InAsSb/InAsSbP diode lasers oscillating at wavelengths of 3.1–3.2 μm. It is established that the contribution of nonradiative recombination to the lasing threshold can be as large as 97%. The internal quantum yield of luminescence for the InAs_0.97Sb_0.03 compound is no higher than 3%. Most likely, the nonradiative channel is formed with involvement of Auger recombination with the constant C = 4.2 × 10^?38 m⁶s^?1 (T = 77 K). The studied samples of lasers feature relatively low optical losses ρ = 900 m^?1 and internal quantum efficiency of emission at the level of 0.6. The spontaneous lifetime of nonequilibrium charge carriers as determined from the radiative-recombination rate is equal to 6 × 10^?8 s, which is consistent with known published data.     

Gain suppression in GaAs/AlGaAs TJS lasers

Experimental results on gain suppression in transverse junetion stripe (TJS) lasers with a heavily doped active region is reported for the first time. These lasers oscillate in the fundamental transverse and lateral modes with gain suppression, and reproducibly operate in a single-longitudinal mode up to 1.8 times the threshold current.     

Very low threshold GaInAsP/InP double-heterostructure lasers grown by LP MOCVD

Room-temperature GaInAsP/InP DH lasers emitting at 1.3 ?m and having very low threshold current densities have been grown by LP MOCVD. Thresholds were lower than the best values reported for comparable devices grown by LPE, the lowest threshold being 430 A/cm2 for a cavity length of 950 ?m (width 150 ?m) with an active-layer thickness of d = 2200 A.     

Narrow-beam divergence of the emission from low-threshold GaInAsP/InP double-heterostructure lasers

The angles of beam divergence perpendicular to the junction plane have been studied for low-threshold GaInAsP/InP double-heterostructure lasers with a thin active layer emitting at 1.31 ?m. The narrowest beam divergence obtained was 23° for a laser diode with an active-layer thickness of 0.05 ?m. At an active-layer thickness of 0.13 ?m, the beam divergence was 40° with a threshold current density of 770 A/cm2.     

TE and TM coupling coefficients in distributed feedback double-heterostructure PbSnTe lasers

TE and TM coupling coefficients for double-heterostructure distributed feedback (DFB) Pb1-xSnxTe diode lasers are calculated. Results are presented for rectangular, sinusoidal, symmetric-triangular, and sawtooth gratings for both intermode and intramode coupling. Based on these results, the design considerations of PbSnTe DFB lasers are also discussed.     

Output coupling for closely confined Pb1-xSnxTe double-heterostructure lasers

The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb1-xSnxTe. For the TEOmode incident at the laser mirror and for thin optical guiding regions such that only the TEO, TE1, TMO, and TM1modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system.     

Strong signal analysis of optical nonlinearities insingle-quantum-well and double-heterostructure lasers

Based on the numerical strong signal solution of the density-matrix formalism, the nonlinearities of the gain and the refractive index are discussed for both bulk double-heterostructure (DH) and single-quantum-well (SQW) InGaAs lasers. The results show that for both structures the nonlinear gain is well approximated by the recently proposed analytical expression and the modified two-level system approximation up to a range of photon density discussed herein, and the refractive index could either increase or decrease with the photon density depending on the wavelength detuning from the gain peak. The results of a new analytical expression for nonlinear refractive index is in qualitative agreement with the numerical ones; however, significant quantitative difference occurs between these two model results for high photon density values. Due to the more important nonlinear gain in SQW structures, the linewidth enhancement factor increases more rapidly with increasing photon density in these structures than in DH structures