We offer GaAs Epitaxial Wafers for Schottky Diode as follows:

Millimeter and submillimeter heterodyne observations will improve our understanding of the universe, the solar system and the Earth atmosphere. Schottky diodes are strategical components that can be used to build THz sources or mixers working at room temperature. A GaAs Schottky diode is one of the key elements for multipliers and mixers at THz frequencies since the diode can be extremely fast by reducing its size and also very efficient thanks to the low forward voltage drop.

The fabrication process presented below is based on electron beam lithography and conventional epitaxial layer designs. The starting material is a semi-insulating 500µm GaAs substrate with epitaxial layers grown by Metal-Organic Chemical Vapor Deposition (MOCVD) or Molecular Beam Epitaxy (MBE).

The layer structure consists of a first 400nm of AlGaAs etch-stop layer and a first GaAs 40µm membrane by a second 400nm of AlGaAs etch-stop layer and a second GaAs thick membrane.

The active parts of the substrates are as , 40nm AlGaAs etch-stop layer, an 800nm heavily doped 5x1018cm-3 n+ GaAs layer and a 100nm n type GaAs layer doped 1x1017cm-3.

Two different structures for mixers, a 183GHz MMIC mixer (Fig 1-a) and a 330GHz circuit mixer (Fig 1-b) have been designed via CAD systems and fabricated using e-beam lithography.

Fig 1: CAD captures of 183GHz MMIC mixer (a) and 330GHz circuit mixer (b).

A selective AlGaAs/GaAs wet etching is used to define the device mesas, the etch rate slows down sufficiently when the etch-stop layer is reached.

For the ohmic contacts, the n+ GaAs layer is recessed, Ni/Ge/Au metal films are successively evaporated and a rapid thermal annealing is performed.

For the air-bridges and Schottky anodes/connection pads, the process is as . Firstly, a square of resist is exposed and reflowed to form the support for the air-bridges.

The anodes are then fabricated using two layers of resists and the required profile is obtained by the combination of resist layer thicknesses, sensitivities and exposure doses.

Finally, Ti/Au metal film is evaporated to make the Schottky contacts and connection pads.

The diodes are then passivated using Si3N4 deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition). To allow circuit integration, circuits are separated by a deep dry etching using ICP (Inductive Coupled Plasma) - RIE: 10µm etching for the 330GHz circuit and 50µm etching for the 183GHz MMIC.

Finally, the wafer is then mounted topside-down onto a carrier wafer by using wax. The semi-insulating GaAs substrate is thinned to the desired thickness (10µm or 50µm) using the same process as in.

Source: semiconductorwafers.net

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