L.L. Goddard

Low-threshold continuous-wave 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs

We present the first continuous-wave (CW) edge-emitting lasers at 1.5 /spl mu/m grown on GaAs by molecular beam epitaxy (MBE). These single quantum well (QW) devices show dramatic improvement in all areas of device performance as compared to previous reports. CW output powers as high as 140 mW (both facets) were obtained from 20 /spl mu/m /spl times/ 2450 /spl mu/m ridge-waveguide lasers possessing a threshold current density of 1.06 kA/cm/sup 2/, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K from 10/spl deg/C-60/spl deg/C. The lasing wavelength shifted 0.58 nm/K, resulting in CW laser action at 1.52 /spl mu/m at 70/spl deg/C. This is the first report of CW GaAs-based laser operation beyond 1.5 /spl mu/m. Evidence of Auger recombination and intervalence band absorption was found over the range of operation and prevented CW operation above 70/spl deg/C. Maximum CW output power was limited by insufficient thermal heatsinking; however, devices with a highly reflective (HR) coating applied to one facet produced 707 mW of pulsed output power limited by the laser driver. Similar CW output powers are expected with more sophisticated packaging and further optimization of the gain region. It is expected that such lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace InP-based lasers for applications from 1.2 to 1.6 /spl mu/m.

On the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers

We analyze the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs. Building on the method of Tansu and coworkers, we find evidence that the characteristic temperatures for the threshold current T/sub 0/ and external efficiency T/sub 1/ are balanced by a combination of monomolecular recombination and temperature destabilizing mechanism(s) near room temperature. At elevated temperatures, the destabilizing process(es) dominate, due to increased threshold current density J/sub th/. While it is difficult to definitively identify carrier leakage, Auger recombination, or a combination of the two as the responsible mechanism(s), results indicate that carrier leakage certainly plays a role. Evidence of intervalence band absorption was also found; T/sub 1/ was reduced, but J/sub th/ and T/sub 0/ were not significantly degraded. Conclusions are corroborated by supporting measurements of the Z-parameter with bias, spontaneous emission spectrum, and band-offsets. Spontaneous emission measurements show evidence of weak Fermi-level pinning within the active region at threshold, indicating a form of carrier leakage. This is consistent with the characteristic temperature analysis and a leakage mechanism is proposed. This process is partially responsible for the greater temperature sensitivity of device parameters and the poor internal efficiency. Methods for reducing the effects of each parasitic mechanism are also described.

1.5 μm GaInNAs(Sb) lasers grown on GaAs by MBE

Abstract We demonstrate the first 1.5xa0μm GaInNAsSb laser grown on GaAs. It exhibits much improved threshold current density as compared with previously reported GaInNAs lasers at 1.52xa0μm. A 1.465xa0μm laser with far superior performance is also demonstrated. This device exhibits a pulsed threshold current density of 930xa0A/cm2 per quantum well, a differential quantum efficiency of 0.30xa0W/A (both facets), an external quantum efficiency of 35%, and peak power above 70xa0mW. Additionally, the use of antimony allows for a decrease in the bandgap out to 1.6xa0μm, while still preserving luminescence efficiency as compared to 1.3xa0μm GaInNAs material.

GaInNAs(Sb) vertical-cavity surface-emitting lasers at 1.460 μm

We demonstrate a top emitting, electrically pumped, GaInNAsSb vertical-cavity surface-emitting laser (VCSEL) grown monolithically on GaAs, lasing pulsed at a wavelength of 1.460 μm, at a chuck temperature of −10u200a°C, with a threshold current of 550 mA (16 kA/cm2) and a duty cycle of 0.1% for large mesas. Dilute nitrides, such as GaInNAs, have proven effective for lasers operating at 1.31 μm, but reaching longer wavelengths has proven difficult due to defects from low-temperature growth, surface roughening, and nitrogen-related defects. Reduction of oxygen contamination and careful attention to plasma conditions allow a similar extension to laser wavelength, by minimizing crystal defects introduced during growth. This is the first VCSEL on GaAs beyond 1.31 μm to date.

MBE Growth and Characterization of Long Wavelength Dilute Nitride III–V Alloys

This chapter provides an insight into the better confinement for electrons and a better match of the valence and conduction band densities of GaAs to a higher operating temperature, higher efficiency, and higher output power to grow 1.3-1.6 μm active quantum. Dilute nitrides or dilute nitride-arsenides are two very different (III-V) semiconductors that differ not only in their electronic properties, but also in their range of miscibility gap in the alloys. The chapter also discusses different crystal structure for the endpoint alloys (zinc blend for in GaAs or GaAsSb versus wurtzite for InGaN) and the methods by which they must be grown. The major challenge for GaInNAs(Sb) is to understand the differences of the dilute nitrides compared to other III-V alloys and to produce low threshold lasers at any desired wavelength between 1.3 and 1.6 μm. The most recent results incorporating Sb to form a GaInNAsSb appear to overcome many of the prior problems with phase segregation.

High-performance GaInNAsSb/GaAs lasers at 1.5 um

We achieved 1.5-um CW SQW GaInNAsSb lasers with GaNAs barriers grown by MBE on GaAs substrates with typical room temperature threshold densities below 600A/cm2, external quantum efficiencies above 50%, and output powers exceeding 200mW from both facets for 20x1222um devices tested epitaxial-side up. In pulsed mode, 450A/cm2, 50%, and 1100mW were realized. Longer devices yielded over 425mW of total CW power and thresholds below 450A/cm2. These results are comparable to high quality GaInNAs/GaAs lasers at 1.3um. Z-parameter measurements revealed that these improvements in the performance metrics of approximately 40-60% over previous results are primarily due to reduced monomolecular recombination. The large differential gain of GaInNAsSb/GaNAs/GaAs lasers at 1.5um of approximately 1.2x10-15cm2 was mostly squandered in previous devices due to large quantities of monomolecular recombination. The characteristic temperatures for threshold current, T0, and for efficiency, T1, were 66K and 132K, respectively. These reduced values, compared to prior measurements of 106K and 208K, respectively, indicate carrier leakage. Since monomolecular recombination is temperature insensitive, the temperature stability of device operation was adversely affected.

Reduced mono-molecular recombination in GaInNAsSb/GaAs lasers at 1.5 /spl mu/m

We present 1.5 /spl mu/m CW GaInNAsSb/GaAs lasers with typical room temperature threshold densities below 600 A/cm/sup 2/, external efficiencies above 50% and output powers of 200 mW. Z-parameter measurements show these improvements are primarily due to reduced monomolecular recombination.

1.55 /spl mu/m GalnNAsSb lasers on GaAs

We present a 1.55 /spl mu/m laser grown on GaAs by molecular beam epitaxy. The active layer was a single GaInNAsSb quantum well surrounded by strain-compensating GaNAs barriers. The room temperature threshold current density was 2.4 kA/cm/sup 2/, lasing at 1.553 /spl mu/m.

Low-threshold CW 1.55-/spl mu/m GaAs-based lasers

We demonstrate the first low-threshold continuous-wave (CW) 1.55-/spl mu/m GaAs-based lasers. Using a single GaInNAsSb quantum well as the active region, edge-emitting lasers yielded CW thresholds as low as 579 A/cm/sup 2/ (550 A/cm/sup 2/ pulsed) and output powers > 100 mW.

Differential gain and non-linear gain compression of GaInNAsSb/GaAs lasers at 1.5/spl mu/m

We present temperature dependent measurements of differential gain, dg/dn, and nonlinear gain compression, /spl epsiv/. At 20/spl deg/C, dg/dn=92/spl times/10/sup -16/cm/sup 2/ and /spl epsiv/=1.4/spl times/10/sup -16/cm/sup 3/. The 57K characteristic temperature of dg/dn limited T/sub 0/. Large /spl epsiv/ caused spectral broadening at high power.