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.<>     

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     

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     

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     

Cryogenic microwave performance of 0.5-μm InGaAs MESFET's

Microwave and DC properties of 0.5-μm InGaAs MESFETs were measured at 300 and 125 K. The authors have measured approximately 30% increases in RF g_m|ext and f_T when cooling from 300 to 125 K. The authors also observe a 0.06-V increase in gate built-in voltage at 125 K that results in smaller gate leakage currents. The improved gate characteristic at 125 K leads to better RF properties at higher gate bias     

Cryogenic performance of double-fused 1.5-μm vertical cavitylasers

The low-temperature performance of vertical cavity lasers (VCL's) is of interest for high-speed data transmission from superconducting and cryogenic semiconductor circuits. Our double-fused 1.5 μm lasers employ a strain-compensated InGaAsP-InP multiquantum-well (MQW) active region that is sandwiched between two AlGaAs-GaAs distributed Bragg reflectors. Continuous wave (CW) lasing at ambient temperature as low as 7 K is measured on the same type of top-emitting devices that previously lased at a record-high temperature of 337 K. The optimum temperature is found at 180 K giving minimum threshold current, maximum modulation bandwidth of 5 GHz, and more than 3 GHz/mA^1/2 modulation current efficiency. The optimum temperature agrees very well with the theoretical prediction. Further device optimization for cryogenic high-speed applications is discussed in detail     

The effect of varying barrier height on the operationalcharacteristics of 1.3-μm strained-layer MQW lasers

This paper presents an empirical study of the effects that barrier layer composition has on the operational characteristics of 1.3-μm-wavelength InGaAsP-InP multiquantum-well (MQW) strained-layer ridge-waveguide lasers. A systematic empirical investigation of how this design choice affects practical device operation was undertaken by examining threshold current, efficiency, and modal gain as a function of temperature in five different laser structures. The results of these studies indicate that small barrier heights improve device performance, despite the loss of electronic confinement in the shallow conduction band quantum wells. Indeed, it appears that carrier uniformity in the MQW structure may be improved by carrier redistribution due to thermal or tunneling effects, which in turn enhances the operation of the low barrier height structures     

Well number, length, and temperature dependence of efficiency andloss in InGaAsP-InP compressively strained MQW ridge waveguide lasers at1.3 μm

Experimental measurements of external differential efficiency on 0.7% compressively strained multiquantum-well (MQW) ridge waveguide lasers operating at 1.3 μm are presented. The lasers have the number of quantum wells (QW's) varying from 5 to 14 and cavity lengths ranging from 250 to 1000 μm and were measured over a temperature range of -50°C to 90°C. A phenomenological model is introduced which shows that over a range of design and operating conditions, the behavior of the external differential quantum efficiency can be entirely explained by intervalence band absorption (IVBA) It is also shown that outside this range IVBA alone is not sufficient to describe the behavior, indicating that current leakage becomes a significant factor. Ramifications of the IVBA contribution to the external differential quantum efficiency are investigated     

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     

Interferometric measurement of the linewidth enhancement factor ofa 1.55-μm strained multiquantum-well InGaAs/InGaAsP amplifier

The linewidth enhancement factor of an InGaAs/InGaAsP strained multiquantum well optical amplifier was measured interferometrically. It varied from 3 to 18 over the wavelength range from 1500 to 1600 nm with injection currents varying from one to four times the lasing threshold of the uncoated device. A rate equation model gave differential gain and refractive index change per carrier, respectively, in the range 0.3 to 2.5×10^-15 cm² and -5 to -8×10^-20 cm³     

Studies of reflection effects on device characteristics and systemperformances of 1.5-μm semiconductor DFB lasers

The effect of the external optical feedback on the 1.5-μm distributed feedback (DFB) laser's device and system performance, both unpackaged and packaged, is studied, considering reflection magnitudes, polarizations, and phases. The reflection is introduced into the laser's AR-coated facet and thus resembles the real system condition for both CW and pulsed (modulated) operations. It is demonstrated that all three parameters can affect the device's CW spectral properties, namely, the emergence of a second mode or mode switching and a clear reflection amplitude dependence on the system performance. When the device is modulated at a subgigabit/second rate, the reflection amplitude is the dominant factor that influences the system performance. Under the assumption that reflection phases do not play a role in inducing a second mode when the reflection level is high and under the worst polarization condition, the percentage of unpackaged lasers failing the CW L-I test under maximum back reflection (-3.55 dB) is low (less than 2%). A similar failure rate was found for the packaged lasers     

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     

Design of the active structure of high-performance 1.55-μm In1-x-yGayAlxAs strained MQW lasers

We have used Harrison's model and the anisotropic parabolic approximation to calculate the band structure of In_1-x-yGa _yAl_xAs compressively strained quantum wells (QWs). To design 1.55 μm wavelength lasers, the relations between the well width, gain, and composition are presented. The well number and the cavity length are optimized to obtain a low threshold and high maximum operating temperature (550-560 K) QW laser. Several empirical formulas are presented for further applications     

Improved performance of 2-μm GaInAs strained quantum-well laserson InP by increasing carrier confinement

We have fabricated and analyzed strained GaInAs quantum-well diode lasers emitting at wavelengths above 2 μm, grown by metal-organic chemical vapor phase epitaxy on InP substrates. To study the effect of carrier confinement on laser performance, lasers grown with nearly lattice matched ternary GaInAs barriers and quaternary GaInAsP barriers were compared. The use of quaternary barriers improves the device performance in terms of output power, emission wavelength, characteristic temperature, differential quantum efficiency, and power efficiency. Internal losses and internal quantum efficiency remain unchanged. At a heat sink temperature of 330 K index guided diode lasers with GaInAsP-barriers emitting at 2.092 μm showed a continuous-wave (CW) output power of 42 mW/facet     

Ten-to-twenty gigabit-per-second modulation performance of1.5-μm distributed feedback lasers for frequency-shift-keying systems

The frequency modulation (FM) and amplitude modulation (AM) responses of a 1.5-μm distributed feedback (DFB) laser were measured to 15 GHz. At 9-mW output power, the magnitude of the FM response was flat out to 12 GHz, and there was a 15-25-ps delay between the FM and AM responses. Computer simulation techniques indicate that the measured FM response is adequate to produce good eye patterns for frequency-shift-keying modulation at data rates up to 20 Gb/s. The high-speed frequency-shift-keying modulation capability of this 1.5-μm DFB laser was experimentally confirmed at 11 Gb/s     

Calculated performances of 1.3-μm vertical-cavitysurface-emitting lasers on InGaAs ternary substrates

1.3-μm vertical-cavity surface-emitting lasers (VCSEL's) on InGaAs ternary substrates are proposed and designed, It is shown that a deep potential well on the ternary substrate enlarges optical gain of a strained quantum well in the wavelength region of 1.3 μm. A higher reflectivity distributed Bragg reflector (DBR) is also obtained by the use of the ternary substrate because materials with a large refractive-index difference can be used for the DBR. Calculated threshold current density of 1.3-μm VCSEL's on the ternary substrates is much lower than those on the conventional InP substrates. The possibility of extremely low threshold current density below 200 A/cm ² and temperature-insensitive operation are described     

Design and performance of externally modulated 1.5-μm lasertransmitter in the presence of chromatic dispersion

Key laser and modulator characteristics that impact the use of externally modulated lasers in the presence of chromatic dispersion, excluding effects due to fiber nonlinearities, are reviewed. After a brief consideration of transmission performance with directly modulated 1.5-μm DFB lasers which have limited application of up to 80 km at 2.5 Gb/s, the key design characteristics of externally modulated transmitters are discussed. Experimental results showing the effects of modulator chirp and laser linewidth at a 2.5-Gb/s transmission rate are presented. It is found that lasers with CW linewidth under 100 MHz have less than 2-dB dispersion penalty for 600 km of non-dispersion-shifted fiber. Lower dispersion penalties can be realized if the modulator chirp is tuned so as to narrow the transmitted pulses. Excellent modulator stability is demonstrated for 60 days of error- and degradation-free 2.5-Gb/s operation     

Absorption loss coefficient of the active layer for 1.48-μm bulkand MQW lasers

It is shown that the absorption loss coefficient of the active layer for 1.48-μm bulk lasers is 66 cm^-1 which is between 45 and 107 cm^-1 for 1.3-μm bulk lasers and for 1.55-μm bulk lasers, respectively. It is also described that the absorption loss coefficient of the active layer for 1.48-μm multiple-quantum-well (MQW) lasers is 28 cm^-1 which is about two-fifths of that for 1.48-μm bulk lasers. Therefore, the high slope efficiency of the 1.48-μm MQW lasers is attributed not only to the small optical confinement factor but also to the small absorption loss coefficient of the active layer     

Low-temperature sensitive, compressively strained InGaAsP active(λ=0.78-0.85 μm) region diode lasers

This letter reports comparative studies between (Al)GaAs versus InGaAsP active region edge-emitting semiconductor lasers for emission wavelength in the IR regime (λ=0.78-0.85 μm). High characteristic temperature T₀(200 K) and T₁ (450 K) edge-emitting diode lasers have been demonstrated by using the compressively strained (Δa/a=0,6%) Al-free (InGaAsP) active region with an emission wavelength of 0.85 μm. The high T₀ and T ₁ a result of low active-layer carrier leakage, will be beneficial for high-temperature and high-power operation. Implementation for InGaAsP-active VCSEL's with compressively strained InGaAsP-active layers and conventional DBR's is also discussed     

High-speed performance of OMCVD grown InAlAs/InGaAs MSMphotodetectors at 1.5 μm and 1.3 μm wavelengths

A report is presented on the fabrication of high-speed In_0.53 Ga_0.47As metal-semiconductor-metal (MSM) photodetectors incorporating a high-quality lattice-matched InAlAs barrier enhancement layer, grown by organometallic chemical vapor deposition (OMCVD). Fast responses of ~55 ps full-width half-maximum at 1.5 μm and ~48 ps at 1.3 μm wavelengths are observed, corresponding to intrinsic device bandwidths of ~8 GHz and ~11 GHz, respectively. The absence of any tail to the pulse response, and of any low-bias DC gain, indicates a low-trap density at the InAlAs/InGaAs heterointerface. Bias independent dark currents of 10-20 μA are observed below breakdown, which occurred at >30 V in devices with a 500-A-thick InAlAs layer