:45pm - 3:OOpm

InAsSb/AlAsSb Double-Heterostructure and InAsSbhAlAs Quantum-Well Diode Lasers Emitting at -4 p m

3.6

H. K. Choi, G. W. Turner, and Z. L. Liau Lincoln Laboratory, Massachusetts Institute of Technology

Lexington, MA 02173-9108, U.S.A.

InAsSb/AlAsSb double-heterostructure lasers emitting at 3.9 pm operated pulsed up to 170 K and cw up to 105 K, with cw power of 30 mW at 70 K. InAsSbflnAlAs quantum-well lasers emitting at 4.5 pm operated pulsed up to 85 K.

Semiconductor diode lasers emitting in the mid-infrared (2 - 5 pm) band are being developed to provide efficient sources for applications such as laser radar, remote sensing, pollution monitoring, and molecular spectroscopy. Diode lasers with GaInAsSb active layers and AlGaAsSb confining layers grown on GaSb substrates are promising for high- performance sources in this spectral region. For lasers emitting at - 2 pm, we have achieved significant improvements in room-temperature performance by employing a GaInAsSb/AlGaAsSb quantum-well (QW) active region and AlGaAsSb cladding layers. Broad-stripe lasers have exhibited pulsed threshold current density Jth as low as 143 A/cm2 and single-ended cw output power as high as 1.3 W [ 11. For lasers emitting at 4 pm, we reported double-heterostructure (DH) lasers with a ternary InAsSb active layer and AlAsSb cladding layers, that operated pulsed up to 155 K and cw up to 80 K [2]. Even though these lasers exhibited better performance than any other 111-V diode lasers with emission wavelengths longer than 3.5 pm, the performance was limited by substantial lattice mismatch in the laser structure. The output power at 80 K was less than 1 mW. In this paper, we report improved InAsSb/AlAsSb DH lasers emitting at -3.9 pm. These devices have operated pulsed up to 170 K and cw up to 105 K, with single-ended cw power of 30 mW at 70 K. In addition, we report preliminary results on the first InAsSb/InAlAs QW lasers emitting at 4.5 pm.

The laser structures were grown on GaSb substrates by molecular beam epitaxy. The DH structure has a 0.8-pm-thick nominally undoped InAsSb active layer, sandwiched between 3-p- th ick AlAsSb cladding layers. Double-crystal x-ray diffraction measurement of the laser structure showed that the lattice match was better than 2.5 x 10-3.

Broad-stripe lasers 60 or 100 pm wide and 500 pm long were fabricated by Si02 patterning. Figure 1 shows the pulsed Jth of a 100-pm-wide device for temperatures between 60 and 170 K. At 60 K, the value of Jth is 36 A/cm2. The characteristic temperature TO for the entire temperature range is 20 K, which is higher than 17 K observed for the previous InAsSb/AlAsSb DH lasers [2]. At the maximum operating temperature of 170 K, the value of is 8.5 kNcm2, which is substantially lower than 24.4 kNcm2 obtained for the previous DH lasers at 155 K [2]. We believe that these improvements are mostly due to careful lattice matching and better growth conditions.

Figure 2 shows the cw output power vs current curves for a 60-pm-wide laser at heatsink temperatures from 80 to 105 K. The maximum power at 80 K is 12.5 mW/facet, with initial differential quantum efficiency of 19% from both facets. Another device 100 pm wide was coated to have high (- 90%) and low (- 10%) reflectivity on the back and front facets, respectively. The maximum power from this device at 40 and 80 K is 30 and 24 mW, respectively.

In order to increase the emission wavelength and improve device performance, we grew a QW structure that has an active region consisting of 15 pairs of compressively

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strained InAsSb wells and tensile-strained InAlAs barriers, surrounded by AlAsSb cladding layers. Calculation of band positions by including strain effects shows that 1InMA.s provides potential barriers to both electrons and holes. Figure 3 shows the pulsed Ja vs temperature of a QW laser. The minimum Jth is 320 Ncm2 at 50 K, and the maximum operating temperature is 85 K. The value of To is 26 K for temperatures between 50 and 70 K. As shown in Fig. 4, the emission wavelength is 4.5 pm, which is the longest value obtained for III-V diode lasers, except for InSb homojunction lasers that operated only at 10 K [3]. Much higher performance is expected for lasers growin under optimum conditions.

This work was sponsored by Phillips Laboratory, the Department of the Air Force.

REFERENCES [l] H. K. Choi, G. W. Turner, and S. J. Eglash, IEEE Photon. Technol. Lett. 6, 7

(1994). [2] S . J. Eglash and H. K. Choi, Appl. Phys. Lett. 64, 833 (1994). [3] I. Melngailis, R. J. Phelan, and R. H. Rediker, Appl. Phys. Lett. 5, 99 (1964).

T E M P E R A T U R E (K)

Fig. 1. Pulsed threshold current density of InAsSb/AlGaAsSb DH laser.

Fig. 2. CW power vs current of InAsSb/ AlAsSb DH laser at several heatsink temperatures.

T loo00

9 L E 1000 pm

i!! E

2 a 9

5

0

w 100 J

40 50 6 0 7 0 8 0 9 0

TEMPERATURE (K)

0 0

I I I I I 1 4.49 4.50 4.51 4.53 4.54

WAVELENGTH ( pm)

Fig. 3. Pulsed threshold current density of InAsSb/InAlAs QW laser.

Fig. 4. Emission spectrum of InAsSb/ InAlAs QW laser.

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