We demonstrate the use of an area selective zinc in-diffusion technique as a simple and efficient technique for the fabrication of integrated photonic devices. In this work, the zinc in-diffusion process has a two fold application. It is well known that the diffusion of zinc in InP follows an interstitial-substitutional diffusion mechanism. This provides a concentration dependent diffusion profile, which allows us to control the sharpness of the diffusion front by controlling the background doping concentration of the semiconductor wafer. By controlling the zinc depth combined with a sharp diffusion front, the insertion losses of the devices can be minimized. In addition, this results in selective definition of p-n junctions across the semiconductor wafer and therefore offers the potential for integration with electronic devices. Using this technique an integrated 2x2 Mach-Zehnder modulator/switch was fabricated. The semiconductor wafer is based on InGaAsP multiple quantum wells. To selectively define p-n regions for the contacts, we use a 200-nm thick silicon nitride mask during the diffusion. The Mach-Zehnder structure is then patterned using photolithography and dry etching. After a cyclotene planarization process, p-type contacts are deposited on top of the diffused regions by evaporation and lift-off. Our experimental results demonstrate that on-chip losses on the order of 4-dB are obtained, which is significantly lower compared to the use of isolation trenches. The device response as a modulator requires an additional insertion loss of 3-dB for voltage controlled operation, with an extinction ratio better than 16 dB. In the case of electrical current operation, better than 20 dB extinction ratio was obtained with only 8 mA.
[1]
R. A. Logan,et al.
Concentration dependent Zn diffusion in InP during metalorganic vapor phase epitaxy
,
1995
.
[2]
Pallab Bhattacharya,et al.
Low‐ and high‐field transport properties of pseudomorphic InxGa1−xAs/In0.52Al0.48As (0.53≤x≤0.65) modulation‐doped heterostructures
,
1988
.
[3]
Bahaa E. A. Saleh,et al.
Breakdown voltage in thin III–V avalanche photodiodes
,
2001
.
[4]
H. Serreze,et al.
Zn diffusion in InP: effect of substrate dopant concentration
,
1986
.
[5]
D. Tjaden,et al.
Zinc diffusion in n‐type indium phosphide
,
1987
.
[6]
A. Sneh,et al.
Compact, low-crosstalk, and low-propagation-loss quantum-well Y-branch switches
,
1996,
IEEE Photonics Technology Letters.
[7]
D. Tjaden,et al.
Interstitial and substitutional Zn in InP and InGaAsP
,
1989
.
[8]
B. Tuck.
Atomic Diffusion in III–V Semiconductors
,
1988
.
[9]
R. Langenhorst,et al.
Fast 2 x 2 Mach-Zehnder optical space switches using InGaAsP-InP multiquantum-well structures
,
1995,
IEEE Photonics Technology Letters.
[10]
Ilgu Yun,et al.
Zinc diffusion process investigation of InP-based test structures for high-speed avalanche photodiode fabrication
,
2000
.
[11]
Erwan Pincemin,et al.
40 Gbit/s polarisation-insensitive and wavelength-independent InP Mach-Zehnder modulator for all-optical regeneration
,
1999
.
[12]
P. Enders,et al.
Rapid thermal processing of zinc diffusion in indium phosphide
,
1992
.
[13]
T. Weng.
A comparative study of p-type diffusion in III-V compound semiconductors
,
1997,
1997 IEEE Hong Kong Proceedings Electron Devices Meeting.