NOVELTY - The semiconductor-based photovoltaic device such as photodiode e.g. solar cell, comprises a contact region, a light-receiving or light-transmitting region, a window layer formed over an n-type layer or a p-type layer of the device, and an anti-reflection coating formed at the light receiving region. The n-type layer and p-type layer form a p-n junction. At the light-receiving or light transmitting region, the window layer provides partial transmission of incident or generated light through to or from the n-type layer or p-type layer in operation.    USE - The semiconductor-based photovoltaic device such as photodiode e.g. solar cell, phototransistor, light-emitting diode or laser diode, is useful in renewable power generation for terrestrial and non-terrestrial applications.    ADVANTAGE - The semiconductor-based photovoltaic device can be effectively produced with high external quantum efficiency by suppressing exposure of the window layer to oxidizing species.    DETAILED DESCRIPTION - The semiconductor-based photovoltaic device such as photodiode e.g. solar cell, comprises a contact region, a light-receiving or light-transmitting region, a window layer formed over an n-type layer or a p-type layer of the device, and an anti-reflection coating formed at the light receiving region. The n-type layer and p-type layer form a p-n junction. At the light-receiving or light transmitting region, the window layer provides partial transmission of incident or generated light through to or from the n-type layer or p-type layer in operation, and promotes reduced carrier recombination at the surface of the n-type or p-type layer and/or partial reflection of minority carriers in the n-type or p-type layer towards the p-n junction. The device has a window protection layer, which is formed over the window layer and provides protection from degradation of the window layer during manufacture and/or operation of the device and protection against degradation by oxidation and/or hydrolysis of the window layer. The antireflection coating is formed over the window protection layer. The window layer and the window protection layer have a thickness of 1.5 mu m and 0.5 mu m respectively. The contact region includes a layer of semiconducting contact material formed over the window protection layer, with an etch-stop layer sandwiched between the layer of semiconducting contact material and window protection layer. The etch-stop layer is formed of a material having an etching rate of 10 times slower than an etching rate of the semiconducting contact material under the same predetermined etchant conditions. The etch-stop layer has a thickness of 10 nm. The thickness of the semiconducting contact material layer is 5 nm. The device includes a substrate and intermediate layers between the substrate and the n-type or p-type layers, where the n-type and p-type layers are epitaxial layers. A band gap energy at the r-point of the window layer is 2.6 eV. An INDEPENDENT CLAIM is included for a method of manufacturing a semiconductor-based photovoltaic device.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross sectional view of a typical single-junction heteroface solar cell.