Patent ID: 9577042
Date: 2017-02-21
CPC Classifications: H01L

Claim:
1. A method, comprising: providing a starting semiconductor structure, the starting structure comprising a semiconductor substrate, an active region comprising a source region, a drain region and a channel region therebetween, and a gate structure above the channel region; in each of the source and drain regions, forming a bottom barrier layer of a first compound semiconductor material; forming a seed layer of a second compound semiconductor material over the bottom barrier layer, the seed layer having a first bandgap; forming a top layer of a third compound semiconductor material above the seed layer, the top layer having a second bandgap that is narrow compared to the first bandgap, wherein each compound semiconductor material comprises at least one semiconductor material from each of Groups III and V of the Periodic Table of Elements; and forming a compositionally graded layer of the second and third compound semiconductor materials between the seed layer and the top layer, the compositionally graded layer gradually transitioning from the second compound semiconductor material at a bottom portion thereof to the third compound semiconductor material at a top portion thereof.