Zhengda Pang

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Engineering Physics


Peter Mascher


John G. Simmons


InP and related materials have become important materials for applications in many electronic and photonic devices because of their high electron mobilities and high saturation electron drift velocities. InGaAs and InGaAsP, grown lattice matched to InP, are the materials of choice for making light sources and detectors in the wavelength range of 1.3-1.6 μm for the present day high data rate, long haul, fibre-optic communication systems. InGaAs metal-semiconductor-metal (MSM) photodetectors, InGaAs high-electron mobility transistors (HEMTs) and their monolithic integration as photoreceivers are promising devices for opto-electronic integrated circuits (OEICs). In the fabrication of the InGaAs MSM-PDs and HEMTs, good Schottky contacts are critical to achieve high performance, such as low dark current and high breakdown voltage, of the devices. However, the Schottky barrier height of metal/InGaAs contacts is only about 0.2-0.3 eV, which is not high enough for device applications. InP was chosen as the contact material in our fabrications of InGaAs MSM-PDs and HEMTs because of its compatibility in growth and lattice matched to In₀₅₃Ga₀₄₇As. In this research, the following investigations were carried out to understand the physics of the InP Schottky barrier, to obtain good Schottky contacts to InP, and to improve the performance of the InP/InGaAs MSM-PDs. (1) It was found that the current-voltage characteristics of metal(s)-InP Schottky contacts depart from the behavior predicted for the thermionic emission model. To explain these barrier anomalies. a modified current-voltage relationship was developed based on the inhomogeneous Schottky barrier. (2) A systematic investigation on metallization schemes shows that the Schottky barrier height of metal(s)-InP ranges from 0.38 to 0.5 eV, depending on the metal(s) and deposition techniques and the surface conditions of the InP. Among them, Au/Ti/Pt produces the highest barrier height while Au/Ni/Pt has the best uniformity in metal(s)-InP Schottky contacts. To further increase the Schottky barrier height, a thin In1-xGxP (x ranges from 0.1 to 0.3) layer of 100-200 Å grown on top of InP was employed. The barrier height obtained is found between 0.56 to 0.65 eV. The dark current is significantly reduced while the reverse breakdown voltage is increased from about 15 V to 20 V. (3) High-performance InGaAs MSM-PDs with InP as the barrier layer was fabricated. The MSM-PDs with a finger width of 2μm, finger spacing of 2μm, and an active area of 50 x 50 μm², have a dark current of about 200 nA at a bias of 10 V, a low capacitance of 0.2 pF, and breakdown voltages of about 15 V. A fairly high responsivity of 0.75±0.05 A/W at λ=1.3 μm was obtained. The temporal response is characterized by a rise time of about 4.0±0.2 ps, fall time of 8.0±0.2 ps, and FWHM of 8.5±0.2 ps which corresponds to a 3-dB frequency (unit current gain cut-off frequency), f3dB, of 20 GHz. The performance is comparable to the best of those InGaAs MSM-PDs with InAlAs as the contact layer. (4) Because of the lateral conduction in MSM-PDs and the Fermi-level pinning in InP due to surface states, the surface conditions play an important role in device performance. Surface passivation using (NH₄)₂Sx solution was successfully implemented to improve the performance of InGaAs/InP MSM-PDs.

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