NOVELTY - The method involves providing a germanium substrate (1) in which a germanium- and tin alloy layer (10) is presented. A stressor layer is deposited on the germanium substrate. A stress is applied from the stressor layer to the germanium substrate in which the stress cleaves the germanium substrate to provide a cleaved surface. The germanium- and tin alloy layer is provided between the stressor layer and the cleaved surface of the germanium substrate. The cleaved surface is selectively etched till to the germanium- and tin alloy layer of the germanium substrate with hydrogen peroxide.    USE - Method for cleaving a semiconductor material for manufacturing a photovoltaic unit (claimed) that is utilized to convert energy of incident photons to electromotive force for producing electrical energy. Uses include but are not limited to aluminum antimonide (AlSb), aluminum arsenide (AlAs), aluminum nitride (AlN), aluminum phosphide (AlP), boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), gallium arsenide (GaAs), gallium phosphide (GaP) and indium antimonide (InSb).    ADVANTAGE - The method enables selectively etching the cleaved surface till to the germanium- and tin alloy layer of the germanium substrate with the hydrogen peroxide such that amount of semiconductor material used to fabricate solar cells can be minimized while increasing energy conversion efficiency.    DETAILED DESCRIPTION - The germanium- and tin alloy layer is formed by molecular beam epitaxy of germanium and tin solid source materials and by chemical vapor deposition of germanium-containing source gas and tin-containing source gas, which consists of stannane (SnH4) and stannane-d4 (SnD4). The stressor layer is selected from a group consisting of a metal containing layer, a polymer layer and an adhesive tape. An INDEPENDENT CLAIM is also included for a photovoltaic unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a side sectional view of a germanium substrate with a germanium- and tin alloy layer that is utilized in a method of forming a photovoltaic unit.    Germanium substrate (1)    Germanium layers (5, 15)    Germanium- and tin alloy layer (10)