B.M. Onat

High bandwidth-efficiency resonant cavity enhanced Schottky photodiodes for 800–850 nm wavelength operation

High-speed resonant cavity enhanced Schottky photodiodes operating in 800–850 nm wavelength region are demonstrated. The devices are fabricated in the AlGaAs/GaAs material system. The Schottky contact is a semitransparent Au film which also serves as the top reflector of the Fabry–Perot cavity. The detectors exhibit a peak quantum efficiency of η=0.5 at λ=827 nm wavelength and a 3 dB bandwidth of more than 50 GHz resulting in a bandwidth-efficiency product of more than 25 GHz.

100-GHz resonant cavity enhanced Schottky photodiodes

Resonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al,In)GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated.

Fabrication of high-speed resonant cavity enhanced Schottky photodiodes

We report the fabrication and testing of a GaAs-based high-speed resonant cavity enhanced (RCE) Schottky photodiode. The top-illuminated RCE detector is constructed by integrating a Schottky contact, a thin absorption region (In/sub 0.08/Ga/sub 0.92/As) and a distributed AlAs-GaAs Bragg mirror. The Schottky contact metal serves as a high-reflectivity top mirror in the RCE detector structure. The devices were fabricated by using a microwave-compatible fabrication process. The resulting spectral photo response had a resonance around 895 nm, in good agreement with our simulations. The full-width-at-half-maximum (FWHM) was 15 nm, and the enhancement factor was in excess of 6. The photodiode had an experimental setup limited temporal response of 18 ps FWHM, corresponding to a 3-dB bandwidth of 20 GHz.

Transient simulation of heterojunction photodiodes-part II: analysis of resonant cavity enhanced photodetectors

The high-speed response properties of resonant cavity enhanced (RCE) photodetectors have been investigated. The limitations on the high-speed performance of photodiodes and the advantages of RCE-detection are discussed. Transient response of heterojunction photodiodes under pulsed optical illumination has been simulated using the method described in Part I. Results on conventional AlGaAs/GaAs and RCE GaAs/InGaAs heterojunction p-i-n photodiodes are presented. For small area detectors, almost 50% bandwidth improvement along with a two-fold increase in efficiency is predicted for RCE devices over optimized conventional photodiodes. A nearly three-fold enhancement in the bandwidth-efficiency product was shown. >

Transient simulation of heterojunction photodiodes-part I: computational methods

A novel approach is presented for incorporating the transient solution of one-dimensional semiconductor drift-diffusion equations within a general circuit simulation tool. This approach allows simple representation of localized carrier transport models of simulated devices through equivalent circuit elements such as voltage controlled current sources and capacitors. It also lends itself to mixed-mode transient simulation of devices and circuits. The utility of the new simulation approach in state-of-the-art device design is demonstrated by the transient response analysis of a GaAs heterojunction p-i-n photodiode, and by the time-domain analysis of an integrated photoreceiver circuit. >

Design and optimization of high-speed resonant cavity enhanced Schottky photodiodes

Resonant cavity enhanced (RCE) photodiodes (PDs) are promising candidates for applications in optical communications and interconnects where high-speed high-efficiency photodetection is desirable. In RCE structures, the electrical properties of the photodetector remain mostly unchanged; however, the presence of the microcavity causes wavelength selectivity accompanied by a drastic increase of the optical field at the resonant wavelengths. The enhanced optical field allows to maintain a high efficiency for faster transit-time limited PDs with thinner absorption regions. The combination of an RCE detection scheme with Schottky PDs allows for the fabrication of high-performance photodetectors with relatively simple material structures and fabrication processes. In top-illuminated RCE Schottky PDs, a semitransparent Schottky contact can also serve as the top reflector of the resonant cavity. We present theoretical and experimental results on spectral and high-speed properties of GaAs-AlAs-InGaAs RCE Schottky PDs designed for 900-nm wavelength.

Polarization sensing with resonant cavity enhanced photodetectors

We describe a new method of sensing the linear polarization of light using resonant cavity enhanced (RCE) photodetectors. The RCE detectors are constructed by integrating a thin absorption region into an asymmetric Fabry-Perot cavity. The top reflector is formed by the semiconductor air interface while the bottom mirror is a distributed Bragg reflector (DBR). Quantum efficiency of these RCE devices can be controlled by tuning the cavity length by recessing the top surface of the detector for off-normal incidence of light the reflectivity of the semiconductor-air interface can be significantly different for TE(s) and TM(p) polarizations. A pair of monolithically integrated RCE photodetectors with cavity lengths tuned for resonance and antiresonance provide a large contrast in response to TE and TM polarizations. An alternative polarization sensor can be formed by vertically integrating a conventional and a RCE photodetector. We show that a large contrast in the TE/TM responsivities of the vertical cavity polarization detectors (VCPD) can be achieved, thus combining detection and polarization sensing in a single mesa semiconductor device. These devices alleviate the problems associated with the bulkiness and critical alignment constraints of the conventional sensors based on polarizing filters or splitters and have potential for fabrication of monolithic smart pixels and imaging arrays.

Ultrafast resonant cavity enhanced Schottky photodiodes

In conclusion, we have demonstrated a high-speed top illuminated resonant cavity enhanced (RCE) Schottky photodiode (PD) with semi-transparent Au contact. The 10 ps FWHM pulses measured on the scope are estimated to represent 4.3 ps FWHM impulse response, corresponding to a 3-dB bandwidth of 100 GHz. The optimized structure is expected to yield a bandwidth-efficiency product larger than 70 GHz.

High-speed resonant-cavity-enhanced Schottky photodiodes

The bandwidth capabilities of optical-fiber telecommunication systems are still not fulfilled with present performances of optoelectronic devices. Schottky photodiode, with 3-dB operating bandwidth exceeding 200 GHz, is one of the best candidates for high-speed photodetection. However, like p-i-n photodiode, Schottky photodiode also suffers from bandwidth-efficiency trade-off. A recent family of resonant-cavity-enhanced (RCE) photodetectors has the potential to overcome this trade-off. In this paper, we report our work on design, fabrication, and testing of high-speed RCE Schottky photodiodes.

Compact polarization sensors with vertically integrated photodetectors

We describe a new method of sensing the linear polarization of light in a single mesa device structure by vertically integrating two photodetectors. The monolithic architecture eliminates the need for several discrete components, such as polarization filters and beam splitters, thus reducing critical alignment requirements and cost for various optical systems. Applications include the simplification of reading heads in magneto-optical (MO) data storage devices and constructing imaging arrays for polarization vision. In imaging, polarization sensing can extract additional information from a scene otherwise not noticeable to the human eye, facilitating remote sensing, material classification, and biological imaging. The operation principle of our vertical cavity polarization detector (VCPD) is based on a resonant cavity enhanced (RCE) photodetector, being vertically integrated with a conventional photodetector. The RCE detector is constructed by integrating a thin absorption region into an asymmetric Fabry-Perot cavity. The top reflector is formed by the semiconductor air interface, while the bottom mirror is a distributed Bragg reflector (DBR). For off-normal incidence of light, the reflectivity of the semiconductor-air interface and DBR are significantly different for TE (s) and TM (p) polarizations. Thus the RCE detector provides resonance enhancement for TE, capturing the TE polarized light in the top detector. For TM polarized light, both reflectivities are small, therefore, light is transmitted to and absorbed in the bottom detector. A large contrast in TE/TM response of the top and bottom detectors is achieved and the linear polarization can be computed from their relative responses. Experimental results displaying good agreement with simulation results have been recently achieved and are presented.