Formation of Devices by Epitaxial Layer Overgrowth

A semiconductor structure comprising:

• a substrate;
• a first semiconductor layer over the substrate, the first semiconductor layer comprising a first p-n junction having a first band gap;
• a second semiconductor layer over the first semiconductor layer, the second semiconductor layer comprising a second p-n junction having a second band gap, the second band gap being greater than the first band gap;
• and
• a third semiconductor layer over the second semiconductor layer, the third semiconductor layer comprising a third p-n junction having a third band gap, the third band gap being greater than the second band gap.

A method comprising:

• forming an insulator layer over a substrate, the insulator layer having an opening to the substrate;
• forming a semiconductor material in the opening of the insulator layer and over a top surface of the insulator layer, the forming the semiconductor material using process conditions that form the semiconductor material in a vertical direction and in a lateral direction;
• and
• while forming the semiconductor material, changing the process conditions such that the semiconductor material is formed in the lateral direction at a greater rate than in the vertical direction.