NOVELTY - The III-nitride based semiconductor device structure comprises a gallium nitride (GaN) substrate or III-nitride layers disposed on the substrate, and III-nitride device layers located above/below the III-nitride layers. The substrate or III-nitride layers include a patterning that reduces crystal defects in deposited III-nitride device layers, as compared to crystal defects in III-nitride device layers deposited on an un-patterned substrate or un-patterned Ill-nitride layer, and the III-nitride layers are semi-polar or non-polar layers. The patterning includes etched mesas.    USE - The III-nitride based structure is useful in a semiconductor device such as optoelectronic device including a light emitting diode and laser diode, a solar cell or an electronic device such as a transistor.    ADVANTAGE - The III-nitride based semiconductor device structure exhibits improved performance.    DETAILED DESCRIPTION - The III-nitride based semiconductor device structure comprises a gallium nitride (GaN) substrate or III-nitride layers disposed on the substrate, and III-nitride device layers located above/below the III-nitride layers. The substrate or III-nitride layers include a patterning that reduces crystal defects in deposited III-nitride device layers, as compared to crystal defects in III-nitride device layers deposited on an un-patterned substrate or un-patterned Ill-nitride layer, and the III-nitride layers are semi-polar or non-polar layers. The patterning includes etched mesas and a hard mask. A thickness and composition of the III-nitride device layers are high enough such that a film, comprising the III-nitride layers and the III-nitride device layers, has a thickness near or greater than the film's critical thickness for relaxation without the patterning. The III-nitride device layers are grown on an un-patterned region of the III-nitride layers or on an un-patterned region of a wafer comprising the substrate or the III-nitride layers. The patterning: forms a pattern with dimensions such that the thickness of the III-nitride device layers at a given composition, before relaxation, is increased by a factor of 4 as compared to without the patterning. The pattern comprises stripes, and a width of each of the stripes in the pattern is 1-50 mu m. An orientation of the pattern is such that the thickness of the III-nitride device layers at a given composition, before relaxation, is increased by a factor of 4. The pattern is oriented parallel to an in-plane projection of a c-direction of the substrate or III-nitride layers. The patterning: is performed on a layer grown on the substrate or the III-nitride layers, reduces or prevents the formation of misfit dislocation lines parallel or inclined to an a-direction of the III-nitride device layers. The III-nitride device layers are layers of a laser diode including cladding layers, wave guiding layers and an active region and layers of a light emitting diode, solar cell or electronic device such as a transistor. The III-nitride device layers above the patterning has a thickness greater than a thickness of similar III-nitride device layers deposited without the patterning, and the device is a fully or partially coherent device with the III-nitride device layers thicker than a normal relaxation thickness limit. The III-nitride device layers comprise a quantum well active region (706) with an indium composition (30%) or an indium composition sufficient to emit light with a peak intensity corresponding to green light. The III-nitride device layers comprise: n-type (704) and p-type (708) InGaN wave guiding layers that are coherently grown with a thickness of 100 nm and an indium composition (10%); a multi quantum well active region, located between the wave guiding layers, with indium gallium nitride quantum wells, where an indium composition of the quantum wells is 10%; and n-type and p-type Gallium Nitride layers, where the n-type and p-type wave guiding layers (702, 710) are positioned between the n-type and p-type GaN layers. The substrate has a threading dislocation density of greater than or equal to 106 cm-2. The misfit dislocation density in the III-nitride device layers is less than or equal to 104 cm-2, and the patterning is located away from an active region of the device. An INDEPENDENT CLAIM is included for a method of fabricating a III-nitride based semiconductor device.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a device structure.    N-type GaN layer (702)    N-type InGaN wave guiding layer (704)    Multi quantum well active region (706)    P-type InGaN wave guiding layer (708)    P-type Gallium Nitride layer. (710)