A SEMICONDUCTING PHOTO ELEMENT AND A METHOD OF MANUFACTURING SAME

Abstract: A semiconducting photo element has an interface between substrate and converting layer, which is provided with a light reflecting surface. A method for manufacturing such element comprises directly bonding the converting layer on the substrate.

Description: In order to achieve high outputs from solar cells, the converting layers of these solar cells should be thin - see EP-A-0071396. Incident radiation on such converting layers should be confined in this converting layer -see also EP-A-0071396. According to EP-A-0071396 the converting layer of a solar cell is deposited onto a reflecting diffraction grating showing a square wave arrangement. From the Conference Record of the 18th IEEE Photovoltaic Specialists Conference, Las Vegas, 21-25 October 1985, pages 192-197, it is known to grow an epitaxial layer onto a textured layer of SiO₂ to improve confinement of the incident light. The present invention provides a method for producing a semiconductor element for converting incident light into charge carriers, comprising the steps of: providing a semiconductor substrate with hollows; providing a converting part of semiconductor material for converting incident light into charge carriers; and bonding the substrate and the converting part together, such that cavities with air inclusions are formed. According to a preferred embodiment of the present invention a wafer of high quality of semiconducting material can be bonded to the substrate and thinned to the required thickness, such that a thin converting layer with high quality results. Further, the present invention provides an element of semiconductor material comprising: a substrate of doped semiconductor material; a converting layer for converting incident light into charged carriers; and a reflecting interface between the substrate and said converting layer; characterised in that the interface comprises cavities with air inclusions, whereby a large difference in the index of refraction between the converting layer and the substrate results. It is noted that the method according to the present invention provides an elegantly simple way of forming a thin converting layer on a thicker substrate, creating a reflecting surface in between. Either a converting layer having the required thickness is applied to the substrate, or the converting layer is thinned after it has been bonded onto the substrate, e.g. by means of etching. Further advantages, features and details of the present invention will become apparent in the light of a description of a preferred embodiment thereof with reference to a drawing, wherein: fig. 1 shows a schematic cross sectional view of a preferred embodiment of the semiconducting photo element according to the present invention; and fig. 2A and 2B show respective diagrams for explaining the preferred embodiment of the method according to the present invention. A p+ substrate is provided with a conducting contact 1 and provided with cavities or hollows 3, 3' for forming of a reflecting structure between the substrate 2 and a converting layer 4 to be applied thereto wherein incident radiation designated schematically with R has to be converted into (minority) charge carriers. The structure 5 is completed by a passivating layer 6 preferably provided with texturization to enable easy connection of the light and electrical contacts 7, 7' in addition to an anti-reflective layer 8 as generally known in the prior art. The P+-layer has for instance a resistivity of approximately 0.03 Ωcm, and the P--converting layer for instance 2 Ωcm. The surface layer resistance amounts for example to 40-200 Ω/□. In the manufacture of the shown preferred embodiment of the present invention (fig. 2A) the part 4 from fig. 1 is bonded directly onto the part 2 of fig. 1, wherein oxidation of both parts has to be prevented. Hereby, cavities 3, 3' with air inclusions are formed herein whereby a large difference in the index of refraction at least partially results between the converting layer 4 and the substrate 2. The converting layer 4 is subsequently thinned down to the required thickness for the converting layer 4, for instance 50 µm and the contacts 7, 7', the passivating layer 6 and the anti-reflective layer 8 are arranged thereon in known manner. It is expected that with the preferred embodiment shown a considerable improvement in output, for example up to 20%, can be obtained from such solar cells, preferably of silicon. Modifications in respect of the shown described embodiment should be apparent; for instance, the technique shown will also be applicable to GaAs solar cells.

Claims: A method for producing a semiconductor element (5) for converting incident light into charge carriers, comprising the steps of: providing a semiconducting substrate (2) with hollows; providing a converting part (4) of semiconductor material for converting incident light into charge carriers; and bonding the substrate and the converting part together, such that cavities (3,3') with air inclusions are formed. A method according to claim 1, wherein the converting part of semiconductor material is subsequently thinned down to the required thickness to serve as a converting layer for converting incident light into charge carriers. An element (5) of semiconductor material, comprising: a substrate (2) of doped semiconductor material; a converting layer (4) for converting incident light into charge carriers; and a reflecting interface between the substrate and said converting layer; characterized in that the interface comprises cavities (3,3') with air inclusions whereby a large difference in the index of refraction between the converting layer (4) and the substrate (2) results.

Inventors: DEMESMAEKER, ELS SUZANNE JOSEFA, NIJS, JOHAN FRANCIS ALBERT
Applicants: INTERUNIVERSITAIR MICROELEKTRONICA CENTRUM VZW
Application year: 1990
Main classification: H01L31
IPC codes: H01L31