Optical bias controlled amplification in tandem Si-C pinpin devices
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Optical bias controlled amplification in tandem Si-C pinpin devices M. Vieira1,2,3, M. A Vieira1,2, P. Louro1,2, M. Fernandes1,2, A. Fantoni1,2, M. Barata1,2 1
Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014 Lisboa, Portugal Tel: +351 21 8317290, Fax: +351 21 8317114, [email protected]. CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. 2
ABSTRACT A monolithic double pi’n/pin a-SiC:H device that combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal is analyzed under different electrical and optical bias conditions at low and high excitation frequencies. Results show that the transducer is a bias wavelength current-controlled device that make use of changes in the wavelength of the background to control the power delivered to the load. Self optical bias amplification or quenching under uniform irradiation and transient conditions is achieved. The device acts as an optical amplifier whose gain depends on the background wavelength and frequency. An optoelectronic model supported by an electrical simulation explains the operation of the optical system. INTRODUCTION There has been much research on semiconductor optical amplifiers [1]. Here, a specific band or frequency need to be filtered from a wider range of mixed signals. Amorphous silicon carbon tandem structures, through an adequate engineering design of the multiple layers’ thickness, absorption coefficient and dark conductivities can accomplish this function. Those devices have a nonlinear amplitude-dependent response to each incident light wave. Under controlled wavelength backgrounds the light-to-dark sensitivity in a specific wavelength range can be enhanced and quenched in the others, tuning a specific band. This paper reports results on the use of a double pi’n/pin a-SiC:H Wavelength Division Multiplex (WDM) heterostructure as an active band-pass filter transfer function dependent on the wavelength of the trigger light and on the electrical and optical applied bias. DEVICE PREPARATION, CHARACTERIZATION AND OPERATION Optical amplifiers were produced and optimized for a fine tuning of a specific wavelength. The active device consists of a p-i'(a-SiC:H)-n / p-i(a-Si:H)-n heterostructure with low conductivity doped layers. The configuration of the device is shown in Figure 1. Experimental details on the preparation, characterization and optoelectronic properties of the amorphous silicon carbide films and junctions were described elsewhere [2]. The thicknesses and optical gap of the thin i'(200 nm; 2.1 eV) and thick i- (1000 nm; 1.8 eV) layers are optimized for light absorption in the Figure 1 Device configuration.
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blue and red ranges, respectively [2]. As a result, both front and back structures act as optical filters confining, respectively, the blue and the red optical carriers. The device operates within the visible range using as optical signa
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