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Efficient Near Infrared Si/Ge Quantum Dot Photo-Detector Based on a Heterojunction Bipolar Transistor

Published online by Cambridge University Press:  10 February 2011

Anders Elfving ,
Mats Larsson ,
Per-Olof Holtz ,
Göran V. Hansson  and
Wei-Xin Ni
Anders Elfving
Affiliation:
Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden
Mats Larsson
Affiliation:
Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden
Per-Olof Holtz
Affiliation:
Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden
Göran V. Hansson
Affiliation:
Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden
Wei-Xin Ni
Affiliation:
Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden
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Abstract

Ge dots embedded in Si offer the possibility of Si-based light detection at 1.3-1.55 μm. In this communication, we report a very efficient photo-detector based on a Si/SiGe heterojunction bipolar transistor structure with 10 Ge dot layers (8 ML Ge each) incorporated in the basecollector junction. The device structures were grown using low-temperature molecular beam epitaxy, and fabricated for both normal and edge incidence with no electrical contact to the base. The processed Ge-dot transistor detectors revealed a rather low dark current density, 0.01 mA/cm2 at -2 V. Photoconductivity measurements were performed at room temperature. At 1.31 μm, responsivity values of 50 mA/W at normal incidence have been directly measured at Vce = -4 V, without involving any rescaling factor due to light coupling. This value is a ∼250-fold increase compared to a reference p-i-n diode with the same dot layer structure, due to the current amplification function of the transistor. For a rib waveguide device, a very high responsivity value of about 470 mA/W (Vce = -4V) has been obtained at 1.31 μm. Measurements were also performed at 1.55 μm, and the photo-response of the waveguide phototransistor was 25 mA/W, which is again a large improvement compared with the reference waveguide photodiode (∼1 mA/W). Moreover, time-resolved photoconductivity measurements have been carried out. The results have indicated that the device frequency performance is primarily limited by the emitterbase junction capacitance.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 770: Symposium I – Optoelectronics of Group-IV-Based Materials , 2003 , I2.2
Copyright
Copyright © Materials Research Society 2003

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