NOVELTY - Method to split and separate layer of desired thickness of crystalline semiconductor material containing optical, photovoltaic, electronic, micro-electro-mechanical system (MEMS), or optoelectronic devices, from thicker donor wafer, involves: using laser irradiation on side opposite to one containing devices or on same side which contains devices, where at least portion of process flow to form devices is performed prior to splitting and separation process; thickness is 1-100 microns; and several layers of crystalline semiconductor material are formed.    USE - As method and laser processing apparatus to split and separate, or separate layer of crystalline semiconductor material containing optical, photovoltaic, electronic, MEMS or optoelectronic devices from thicker donor wafer; and to transfer layer of crystalline semiconductor material containing optical, photovoltaic, electronic, MEMS, or optoelectronic devices, from donor wafer to substrate or superstrate; which are useful to form separate thin silicon layer for solar cell application, where solar cell is all back contact, back junction solar cell; front-contact solar cell; or bifacial, or front and back contact solar cell (all claimed).    ADVANTAGE - The methods allow controlled micro-crack formation in electric, photonic, mechanical, and optoelectronic devices on surface of wafers, by laser splitting, rater than back-lapping and/or grinding for thin packaging or three-dimensional stacking. The method to transfer layer of desired thickness of crystalline semiconductor material containing optical, photovoltaic, electronic, MEMS, or optoelectronic devices, from donor wafer to another substrate or superstrate, by using laser irradiation, can be performed as part of process flow to form corresponding devices, as laser irradiated separation layer contains crystallographic inhomogeneity, and/or cavities; and separation semiconductor layer to be irradiated containing donor or acceptor dopants with higher density than device layer for wider bad gap semiconducting material is used. By employing method to separate layer of crystalline semiconductor material from thicker donor wafer, by using laser irradiation, donor wafer, such as sapphire wafers having semiconductor PN junction for light emission diode with GaN, GaAlN, InGaN, GaAs, GaAlAs and related compound semiconducting layers or device comprising compound semiconductor PN junction(s) with dissimilar handler, for photovoltaic conversion of light to electrical energy; wafer can be used multiple times for forming several devices and based on several layer separations, as thickness is reduced by laser splitting after device processing and before packaging devices, and reduces production cost. The laser irradiation method allows separation of thin silicon layer for solar cell application, so that silicon layer is transferred to handling substrate or superstrate for further processing to form cell and incorporation in solar cell module. The method by using laser irradiation increases effective throughput of laser splitting/cleaving tool for splitting and separation of material layer from donor wafer by forming two-dimensional array of non-overlapping buried microcracked spots sharing common crystallographic or cleavage plane(s), followed by stress-induced microcrack propagation and interconnection between buried microcracked spots along crystallographic or cleavage plane to cleave and lift off semiconductor layer; as density of non-overlapping buried microcracked spots is made higher at edge(s) of donor wafer to facilitate subsequent separation of material layer. The laser processing system for splitting and separation of layer of semiconducting material from donor wafer by focusing laser beam inside wafer and scanning also maximizes throughput of system; such that system is equipped with multiple stages; system processes multiple wafers simultaneously; and system has several work stations that allow for wafer movement with parallel processing.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) laser processing apparatus to split and separate layer of desired thickness of crystalline semiconductor material containing optical, photovoltaic, electronic MEMS, or optoelectronic devices, from thicker donor wafer, by using laser irradiation on side opposite to one containing devices or on same side which contains devices, where at least portion of manufacturing process flow for fabrication of devices is performed prior to splitting and separation process; desired thickness is 1-100 microns; and several layers of desired thickness of crystalline semiconductor material are produced from thicker donor wafer;    (2) method to transfer layer of desired thickness of crystalline semiconductor material containing optical, photovoltaic, electronic, MEMS, or optoelectronic devices, from donor wafer to another substrate or superstrate, involving: using laser irradiation on side opposite to one containing devices or on side containing devices;    (3) method to separate layer of crystalline semiconductor material of desired thickness containing optical, electronic or optoelectronic devices, from thicker bulk, involving: using laser irradiation focused within bulk and safe distance away from devices such that devices are not affected; where separation plane is chosen to be crystallographic plane of highest atomic density and widest separation from another such plane; separation plane is highest atomic density crystallographic plane, with longest distance between the planes; separation plane is (111) in case of single crystal silicon donor wafer; and laser beam absorption is increased by doping and/or alloying to lower energy band gap relative to rest of bulk material;    (4) laser system configuration with multiple stations to facilitate simultaneous pre-measurement of wafer edge, height of wafer, and roughness and reflectivity of surface being irradiated, which are measured and fed to scanner and laser power controls for real time control of laser focus and uniform power at focus;    (5) method to transfer device layer formed by the laser splitting methods by applying mechanical vibrational forces, inserting wedges, and shear stress for bonded substrates with handler after or during laser irradiation;    (6) method to transfer device layer formed by the laser splitting methods by applying thermal annealing, water jet, chemical jet, and gas jet in conjunction with laser beam through transporting medium or bonded substrates with handler after or during laser irradiation; and    (7) laser splitting method and tool for material layer to transfer where splitting layers consisting of light absorption layers by doping and/or alloying in which band gap is lowered than rest of substrate are formed.    DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional diagram of device layer separation by laser splitting method.