Session 10 Heterojunctions

In the discussion of pn junctions in the previous lessons，we assumed that the semiconductor material was homogeneous throughout the entire structure. This type of junction is called a homojunction . When two different semiconductor materials are used to form a junction，the junction is called a semiconductor heterojunction . When the two semiconductors have the same type of conductivity，the junction is called an isotype heterojunction . When the conductivity types differ，the junction is called an anisotype heterojunctionwhich is a much more useful and common structure than its counterpart.

A growing number of modern devices are based on semiconductor heterojunctions. Modern bipolar transistors employ a p-n heterojunction in order to improve the emitter injection efficiency，while in HFET technology a heterojunction is used to form a high mobility channel.

The heterojunction diodes offer a wide variety of important applications for laser diodes，light-emitting diodes（LEDs），photodetectors，solar cells，junction field-effect transistors（JFETs），modulation-doped field-effect transistors（MODFETs or HEMTs），heterojunction bipolar transistors（HBTs），quantum cascade lasers，quantum well infrared photodetectors（QWIPs），quantum dot lasers，and quantum dot infrared photodetectors. With recent advances in MOCVD and MBE epitaxial growth techniques for Ⅲ-Ⅴ compound semiconductors and SiGe/Si systems，it is now possible to grow extremely high-quality Ⅲ-Ⅴ heterojunction structures with layer thickness of 100 or less for quantum dots，superlattices，and multiquantum-well（MQW）device applications. 1. With recent advances in MOCVD and MBE epitaxial growth techniques for Ⅲ-Ⅴ compound semiconductors and SiGe/Si systems，it is now possible to grow extremely high-quality Ⅲ-Ⅴ heterojunction structures with layer thickness of 100 or less for quantum dots，superlattices，and multiquantum-well（MQW）device applications. 提示：在翻译时，extremely high-quality Ⅲ-Ⅴ heterojunction和layer thickness of 100 or less都可以作为structures的定语。