We investigate the device physics of novel GaAs waveguide photodetectors with integrated photon multiplication. Such detectors have the potential to achieve simultaneously high saturation power, high speed, high responsivity, and quantum efficiencies above 100%. Our device design vertically combines a bulk photodetector ridge waveguide region with laterally confined quantum wells for amplification. Measurements on the first device generation show quantum efficiencies of only 56%. Advanced device simulation is employed to analyze these devices and to reveal performance limitations. Excellent agreement between simulations and measurements is obtained. Device design optimization is proposed, promising more than 700% efficiency.

In this paper, the authors show how selective undercut etching of InGaAs- and InGaAsP-based quantum wells (QWs) can improve the performance of InP-based optoelectronic devices. First, wet-chemical-etching characteristics are investigated. Mixtures of sulphuric and hydrogen peroxide acids are used as wet-etching solutions, and properties such as etch rates, selectivity, and anisotropy are studied in detail. Problems arising from the anisotropic nature of the etching are analyzed, and their impact on device design and performance is discussed. Second, the authors present several optoelectronic devices where selective undercut etching of InGaAs- or InGaAsP-based multiquantum wells (MQWs) improves device performance; these devices include electroabsorption modulators (EAMs), vertical-cavity semiconductors optical amplifiers (VCSOAs), and waveguide amplifier photodetectors (WAPs). Very high extinction ratios were obtained for the EAM. A selective undercut-etched VCSOA reached a record-high 17-dB fiber-to-fiber gain, and the WAP demonstrated an external quantum efficiency higher than 100%.

Traveling-wave photodetectors (TWPDs) are an attractive way to simultaneously maximize external quantum efficiency, electrical bandwidth, and maximum unsaturated output power. We review recent advances in TWPDs. Record high-peak output voltage together with ultrahigh-speed performance has been observed in low-temperature-grown GaAs (LTG-GaAs)-based metal-semiconductor-metal TWPDs at the wavelengths of 800 and 1300 nm. An approach to simultaneously obtain high bandwidth and high external efficiency is a traveling-wave amplifier-photodetector (TAP detector) that combines gain and absorption in either a sequential or simultaneous traveling-wave structure.