The electrical and photovoltaic properties of tunnel metal-oxide-semiconductor devices built on n-InP substrates

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Abstract
Pd‐(n‐type) InP Schottky barrier devices have been fabricated on unoxidized and oxidized surfaces and their electrical as well as photovoltaic characteristics have been evaluated. Devices built on the oxidized surfaces show considerably improved characteristics compared with those built on unoxidized surfaces. A saturation current density of 9×10−9 A cm−2 and barrier height of 0.85 eV have been observed for tunnel Metal‐Oxide‐Semiconductor (MOS) devices compared with 1.1×10−6 A cm−2 and 0.62 eV for Metal‐Semiconductor (MS) devices. Effective Richardson constants, obtained from activation energy plot of saturation current density, have been found to be 0.66 and 1.9 A cm−2 K−2 for MOS and MS devices, respectively. Such low values of the Richardson constant, when compared with the theoretical value, provide clear evidence of the modification of current transport mechanism in the presence of an interfacial layer. Photovoltaic cells with an efficiency of 7% have been built on oxidized surfaces without the use of a grid structure or antireflection coatings. Under AMl illumination, the oxidized devices show the following parameters: open circuit voltage = 575 mV, short circuit current = 16.8 mA/cm2, and fill factor = 0.73. Using photoresponse techniques, the diffusion length has been calculated to be 1.78 μm for MOS devices, a value similar to that obtained for MS devices.

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