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Dosage Effects on Oxygen Implanted Single-Bonded 1.3 pm Vertical-Cavity Surface-Emitting Lasers

J. Zhang, Y. Qian, 2. H. Zhu, Y. H. Lo School of Electrical Engineering, Cornell University, Ithaca, NY 14853

D. L. Huffaker, D. G. Deppe Department of Electrical and Computer Engineering, University of Texas, Austin, TX 78’712

H. Q. Hou, B. E. Hammons Sandia National Laboratories, Albuquerque, NM 87 185

W. Lin, Y. K. Tu Telecommunication Laboratories, Chunghwa Telecom Company, Taiwan, China

1.3 pm vertical-cavity surface-emitting lasers (VCSELs) will have important applications in local access optical networks and high-speed data links. In our earlier paper, we reported low cw threshold current 1.3 pm VCSELs which contain InGaAlAs strain-compensated quantum wells, bonded GaAs/AlGaAs Bragg mirrors, and oxygen implanted current confinement regions [l]. It is believed that oxygen implantation is the key for low threshold current because oxygen atoms have less lateral and vertical straggling than hydrogen atoms and the implanted region can preserve its high resistivity after high temperature wafer-bonding. In this paper we report our studies of the oxygen dosage effects on 1.3 pm VCSELs. We have measured the threshold current, slope efficiency, and series resistance for VCSELs with two different oxygen doses but otherwise the same structure.

Figure 1 shows the VCSEL structure. The device processing is described in detail in the reference [1]. To obtain the proper high resistivity profile in the GaAs/AlGaAs Bragg mirror, oxygen ions were implanted at two energies. The high dosage sample was first implanted at 125 keV with an oxygen dosage of 6x 1 0j4 cm-* and then at 1 10 keV with a dosage of 1 . 5 ~ 1 014 cm”. The low dosage sample was implanted at 125 keV with a dosage of 1 . 5 ~ 1014 cm.’ and then at 110 keV with a dosage of 7 . 5 ~ 1 0 ’ ~ cm-‘. The implantation was performed before bonding the Bragg mirror to the 1.3 pm quantum wells, so the oxygen implanted regions were annealed at the bonding temperature (about 560°C).

Figure 2 shows the dependence of the pulsed threshold cuiTent on device size for both samples. The VCSELs with the lower oxygen dosage show consistently lower threshold currents. Figure 3 shows the P-I slope efficiency of the VCSELs. The devices with the lower oxygen dosage have an average of about 7 dB higher slope efficiency than those with the higher dosage. In addition, VCSELs with the higher dosage did not lase if the device diameter was less than 6 pm. We also measured the differential resistance at a fixed bias voltage for both samples. The VCSELs with the lower dosage always have a lower series resistance. All of these studies suggest that the higher oxygen dosage that we chose in our experiment has introduced excessive optical loss responsible for the relatively poor device performance. Both types of devices seem to have similar lateral current confinement characteristics, although it IS not clear at this moment why the high dosage devices have a higher series resistance. Our study shows that, among othei-

426 0-7803-3895-U97/$10.00 01997 IEEE

parameters, oxygen dosage is an important parameter to optimize in order to achieve high performance 1.3 pm VCSELs.

[I1 Lin.

Y.Qian, Z. H. , and Y. K. Tu,

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Zhu, Y. H. Lo, D. L. Huffaker, D. G. Deppe, H. Q. Hou, B. E. Hammons, W. Appl. Phys. Lett. 71(27), 7 July 1997.

Light output

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Fig. 1. Schematic of 1.3 pm oxygen-implanted VCSELs.

Aperture Diameter (pm)

Fig. 2. Dependence ofthreshold current on aperture diameter of 1.3 pm VCSELs with different oxygen implantation dosages.

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5 10 15 20

Aperture Diameter (pm)

Fig. 3. Dependence of slope efficiency on aperture diameter of 1.3 pm VCSELs with daerent oxygen implantation dosages.

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