Germanium phototransistor with floating body
A floating body germanium (Ge) phototransistor and associated fabrication process are presented. The method includes: providing a silicon (Si) substrate; selectively forming an insulator layer overlying the Si substrate; forming an epitaxial Ge layer overlying the insulator layer using a liquid phase epitaxy (LPE) process; forming a channel region in the Ge layer; forming a gate dielectric, gate electrode, and gate spacers overlying the channel region; and, forming source/drain regions in the Ge layer. The LPE process involves encapsulating the Ge with materials having a melting temperature greater than a first temperature, and melting the Ge using a temperature lower than the first temperature. The LPE process includes: forming a dielectric layer overlying deposited Ge; melting the Ge; and, in response to cooling the Ge, laterally propagating an epitaxial growth front into the Ge from an underlying Si substrate surface.
1. A floating body germanium (Ge) phototransistor, the phototransistor comprising:
a silicon (Si) substrate with a first surface and a second surface;
an insulator layer overlying the Si substrate first surface, exposing the Si substrate second surface;
an epitaxial Ge layer overlying the insulator layer and the Si substrate second surface;
a channel region in the Ge layer;
a gate dielectric, gate electrode, and gate spacers overlying the channel region; and,
source/drain regions in the Ge layer.
2. The phototransistor of claim 1 wherein the epitaxial Ge layer has a thickness in the range of 20 to 1000 nm.
3. The phototransistor of claim 1 wherein the insulator layer has a thickness in the range of 10 to 500 nanometers (nm).
4. The phototransistor of claim 1 wherein the gate dielectric, gate electrode, and gate spacers are formed from wide bandgap materials.
5. The phototransistor of claim 4 wherein the gate dielectric is a material selected from the group including SiO2, GeO2, Al2O3, HfO2, ZrO2, TiO2, Ta2O5, and combinations of the above-mentioned materials;
wherein the gate electrode is a material selected from the group including polycrystalline Ge, polycrystalline SiGe, and polysilicon; and,
wherein the gate spacers are a material selected from the group including SiO2 and Si3N4.
6. The phototransistor of claim 1 wherein the epitaxial Ge layer includes a deep source region between the source and the Si substrate second surface implanted with ions to electrically isolate the Ge layer from the Si substrate second surface.