Novel InP/GaInAs MSM Photodetector for Integration in HEMT Circuits

We report on the investigation of the optoelectric properties of a Metal-Semiconductor-Metal (MSM) photodetector (PD) based on two-dimensional electron gas (2DEG). The layer sequence is compatible to an Al-free High Electron Mobility Transistor (HEMT) layer stucture in the InP/GaInAs material system [1]. Therefore our device can easily be integrated into HEMT circuits. The photoresponse of the MSM-2DEG photodetector was measured by an optoelectric rf-equipment and an electro-optic laser sampling equipment. With the rf equipment we measured a Full Width at Half Maximum (FWHM) of about 60ps at 1.3?m wavelength. The -3dBopt bandwidth was limited by parasitics to 3.8GHz. The value of the dc responsitivity was 0.4A/W without an antireflexion coating. The laser sampling measurements were performed at 875nm and 890nm, and a FWHM of about 1ps. was found. To proof our concept of simple integration, HEMTs were processed on the same wafer with gatelengtis in the range from 1.5?m to 0.2?m. Cutoff frequencies fT=45GHz and fmax=85GHz were measured on a 0.35?m gatelength device.