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High Performance 1.3 pm Vertical-Cavity Surface-Emitting Lasers with Oxygen- Implanted Confinement Regions and Wafer-Bonded Mirrors.

Y. Qian’, Z.H. Zhu’”, Y.H. Lo’, D. L. Huffaker’, D. G. Deppe’, H. Q. Hou3, B.E. Hammons3, W. Lin4, and Y.K. Yu4

* On leave from Zhejiang University, Hangzhou, China 310008 School of Electrical Engineering, Cornell University, Phillips Hall, Ithaca, NY 14853

Department of Semiconductor Materials, Sandia National Laboratories, Albuquerque, NM 871 85 Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78712-1084 Telecommunication Laboratories, Chunghwa Telecom Co., Taiwan

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Summary

Long wavelength (1.3 pm and 1.55 pm) vertical-cavity surface-emitting lasers (VCSELs) are promising candidates for low cost, high performance light sources for optical communications and data links. We recently demonstrated a new structure for long wavelength VCSELs [ l ] where oxygen ions were implanted into a GaAs/AlGaAs mirror to form current confinement regions before wafer- bonding the GaAs/AIGaAs mirror with the AlGaInAdInP cavity layers. This structure is easy to fabricate and a very low threshold current and threshold current density has been achieved for continuos-wave (cw) operation at 20°C [I]. Based on a similar design, we now obtain a record low pulsed threshold current density less than 500 Ncm2 and a pulsed threshold current of 0.83 mA at 20”. The devices can operate up to 40°C under cw condition and above 100°C under pulsed condition.

Fig. 1 shows schematically the oxygen-implanted VCSELs. The devices consist of an oxygen- implanted p-GaAs/AlGaAs (28 pairs) mirror, AlGaInAs/InP strain-compensated multiple quantum well (SC-MQW) cavity layers, and a top ZnSe/MgF (6 pairs) dielectric mirror. The fabrication process is the same as in Ref. 1. The AlGaInAs SC-MQWs consist of nine 53 A wells and ten 87 A strain compensated barriers. Oxygen-implantation was performed to form current blocking regions in the p-GaAs/AlGaAs mirror before the p-mirror was wafer-bonded to the p-InP spacer of the cavity layers. After removal of the InP substrate and the InGaAs etch stop layer, metal ohmic contacts were made and then the ZnSe/MgF dielectric top mirror was formed by E-beam evaporation and lift-off process.

The devices were tested on a copper stage without heat sink. The output light was collected from the top dielectric mirror. Fig. 2 shows the dependence of threshold current density on device dimension under pulsed operation at 20°C. The lowest threshold current density of 454 A/cm2 was detected on a 41 pm diameter device, which is the best result for long wavelength VCSELs. The lowest threshold current is 0.83 mA measured from a 5 pm diameter device, which is the smallest size in our design. As a comparison, in a similar structure but using proton-implantation through the quantum wells into the p-GaAs/AlGaAs bottom mirror, the lowest pulsed threshold current (2 mA) was found on a 15 pm diameter device [2]. This indicates that oxygen-implantation gives rise to lower optical loss so works better for smaller devices. However, the thermal effect prevents the 5 pm device from cw operation at room temperature, and the lowest room temperature cw threshold current of 1 mA was realized on a 9 pm diameter device [I]. The devices also achieved excellent temperature characteristics as shown in Fig.3. The devices can operate up to 110°C under pulsed condition. It is noteworthy that the variation of the threshold currents from 15OC to 60” is smaller than 1 mA. However, junction heating has limited the maximum cw operation temperature to 40°C. With a reduced threshold voltage and resistance in the GaAs/AlGaAs mirror and a better alignment between the cavity mode and the quantum well gain peak, cw operation at a much higher temperature should be achievable.

[I] Y. Qian, Z.H. Zhu, Y.H. Lo, H.Q. Hou, B.E. Hammons, D.L. Huffaker, D.G. Deppe, W. Lin , and Y.K. Tu, Conference Digest of OFC’97, Postdealine Paper, PD-14, Dallas, Februray 1997. [2] Y. Qian, Z.H. Zhu, Y.H. Lo, D.L. Huffaker, D.G. Deppe, H.Q. Hou, B.E. Hammons, W. Lin, and Y.K. Tu, IEEE Photon. Tech. Lett. (to be published).

Light output

Si02

Bonded interface

0+-implant

6-7 5 E 0

4 W

Ge AuNiAu 1 I ZnSeMgFmirror

n-InP

AlGaInAs SC-MQWS

p-InP

CrAu

Fig. I . Schematic cross-section of a single-bonded VCSEL with oxygen-implanted current confinement. The oxygen implantation was performed directly in the p-GaAs/AIGaAs mirror before wafer bonding.

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3 1 0 d

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Diameter = 9 pm Pulsed:

6 1 kHz, 200 ns L I

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15 %

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Device Diameter (pm) Temperature ("C)

Fig. 2. Device diameter dependence of pulsed threshold current desity at room termperature. The lowest threshold

Fig. 3. Temperature dependence of pulsed threshold current and slope efficiency of a 9 pm diameter

current density is 454 Ncm2 on a 41 pm diameter device.

device. The device can operate above 100°C.

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