IEEE PHOTONICS TECHNOLOGY LETTERS. VOL. 3. NO.6. JUNE 1991;70

Abstract-An ultrafast GaAs Schottky pbotodiode is mono-litbically integrated with an aJl-electronic sampler. Tbe higb-speed pbotodiode-electronic-sampling circuit has a temporal response of 2.0 ps full-width-at-balf-maximum (FWHM) corre-sponding to a 3-dB bandwidtb of 150 GHz. Tbe pbotodiode bas an external quantum efficiency of 33OJo. To our knowledge. tbis is the fastest pbotodiode ever reported. Fig. 1 Diagram showing the cross section of the 5 x 5 IJ.m2 semi-trans-parent Schottky photodiode. INTRODUCl10N H IGH-SPI;:ED photodetectors play an important role in optical communication and measurement systems. In a communication system, the use of faster detectors could enhance the system bandwidth, increasing information trans-mission capacity.In a measurement system, they could re-place autocorrelation and cross-correlation techniques which require deconvolution methods since the pulse wavefonn is not directly measured. In order to make high-bandwidth or equivalently high temporal-resolution measurements, it is essential to have high-speed photodetectors with good respon-sivity.Photodetectors are made from many different materi-als, but only GaAs and InGaAs devices have been used as high-speed detectors. GaAs devices are sensitive only for wavelengths shoner than 890 Dm. For longer wavelength high-speed applications, InGaAs photodetectors are used. Wang and Bloom [I] were the first to demonstrate a GaAs photodiode with a 3-dB bandwidth exceeding 100 GHz and a temporal response of 5.4 ps. Later, Parker et al. [2] suc-ceeded in achieving up to 110 GHz performance. For InGaAs photodetectors, Wey et al. [3] reponed a 3.8 ps FWHM. In addition, they reponed the hybrid integration of their InGaAs photodetector and GaAs sampling circuit. All these results have been limited by their measurement techniques. The speed of the actual device had to be indirectly detem1ined by a deconvolution of the system response from the measured data. In order to overcome these measurement problems, we have pursued a monolithic approach [4], [5]. A GaAs based a1l-electronic sampler is monolithically fabricated with a high-speed Schottky photodiode. Without deconvolution, we are able to measure a temporal response of 2.0 ps FWHM, corresponding to a 3-dB bandw!dth of 150 GHz