Glossary
AlGaAsAluminum Gallium Arsenide – a ternary alloy of III-V compound semiconductors with a bandgap increasing with Al content. A layer may be used in HEMTs to create a heterojunction with a GaAs layer through which electrons can move at very high speeds.
BandgapThe energy difference between valence and conduction bands of semiconductor materials. This parameter defines the electrical properties of a semiconductor material (carrier mobility, free carrier density, temperature behavior). Epitaxy of compound semiconductors is used to engineer bandgaps.
Compound semiconductorsAny semiconductor material consisting of two or more material elements from groups III and V or groups II and VI of the Periodic Table (elemental semiconductors such as silicon and germanium are found in group IV). The Roman numerals refer to columns in the Periodic Table. These columns (I, II, III and so forth) denote groups of elements having similar chemical properties. All semiconductors are either in group IV (the carbon family), or are made from compounds of elements in columns at an equal distance from column IV, such as III-V or II-VI. The advantages of compound semiconductors are that they can: convert microwaves to electrical signals in real time; convert electrical energy into light; and withstand radiation and extreme temperatures.
EpitaxyAny process by which a single crystal layer of a material is grown on top of a substrate. When the grown layer is identical to the substrate material, the epitaxy is referred to as homo-epitaxy (mostly used in silicon material applications). Hetero-epitaxy, which refers to growth of a given single crystal material on a different material, is mostly used in compound semiconductor applications.
FETField Effect Transistor – while the most common type of device fabricated in silicon semiconductor manufacturing is the CMOS FET (complementary metal oxide semiconducting FET), compound semiconductors use different kinds of FETs. New types of FETs are expected to become more important in upcoming device generations.
GaAsGallium Arsenide – a III-V compound semiconductor that has been used in making FETs since the 1970’s. Its advantages in device and laser fabrication include very high speeds and switching, as well as very low power consumption and luminescence, thanks to the extremely high carrier mobility.
GaAsSbGallium Arsenide Antimonide - a ternary semiconductor compound where Sb is used to engineer the bandgap energy.
GaNGallium Nitride – a III-V semiconductor compound. Picogiga has demonstrated the feasibility of growing AlGaN/GaN on epilayers on Si for advanced RF and radar applications. In combination with other epilayers, it is also very promising for LEDs.
HBTHeterojunction bipolar transistor – a high-mobility, compound semiconductor bipolar transistor used in RF and radar applications.
HEMTHigh electron mobility transistor – first developed in the 1970’s, it is becoming especially important in advanced communications applications. Fabrication of a HEMT device is based on FET architecture but requires a very precise, lattice-matched heterojunction between two compound semiconductor layers. MBE is the primary technique for creating the layers. The first HEMTs were formed using GaAs and AlGaAs. However new structures using GaN, InGaAs/InAlAs on InP, and SiGe are also gaining attention.
HFETHeterostructure FET (another term for HEMT).
III-V materialsBinary or ternary alloys made from elements in the III and V columns of the Periodic Table. These alloys are semi-conductive. (Elements from groups III and V are also used to dope group IV semiconductors, forming the positive (p) and negative (n) junctions.) Picogiga specializes in III-V compound semiconductors.
InGaPIndium gallium phosphide – a ternary alloy from III-V materials used as a semiconductor compound material. Its usage relates mainly to HEMT and HBT structures.
InGaAsIndium Gallium Arsenide - a ternary alloy from III-V materials used as a semiconductor compound material for channel layers of HEMT devices. The In content determines the two-dimensional carrier density.
InPIndium phosphide – a III-V semiconductor compound.
MBEMolecular Beam Epitaxy – a type of epitaxy that typically grows a crystal lattice-matched, single layer of atoms of a given element onto a monocrystalline substrate. The MBE process used by Picogiga starts with solid sources of ultra-pure elements that are heated in separate furnaces. They evaporate then condense on the wafer. The term “beam” refers to the fact that the different elements only come into contact with each other once they are on the wafer. The furnaces are shuttered open and closed by a computer control system, so that only a single layer of atoms is grown at a time. This enables the formation of very precise, complex structures of layers. “Molecular” is a term used for historic reasons, even though now almost all the layers are atomically grown (except for arsenic, which is still grown in a molecular form).
MESFETsMetal-semiconductor field effect transistor – a device in which the p-n junction is substituted by a Schottky barrier.
mHEMTMetamorphic high-electron mobility transistor – Due to the high content of a third element in a ternary alloy, the hetero-epitaxy of a ternary alloy on GaAs substrate requires a transition layer between the substrate and the epitaxially grown layer. This transition layer aims to relieve intrinsic material stress due to lattice mismatch between materials.
Millimeter WavesFrequency domain where wavelengths are in the millimeter range.
MOVPEMetal organic vapor phase epitaxy – an alternative to MBE for growing compound semi-conducting materials and structures.
pHEMTPseudomorphic high-electron mobility transistor – the compound materials used for pHEMTs are not lattice-matched.
QWIPQuantum Well Infrared Photodetector – a nanodevice for long wavelength focal plane array applications.
RFRadio Frequency (often used synonymously with “wireless”) – Frequency domain above a few hundred hundred MHz.
SiCSilicon Carbide – a ceramic, III-V compound with high thermal conductivity, expected to play a significant role in high-power devices, LEDs, diodes and MESFETs.
Smart Cut™Soitec’s proprietary cleaving/transfer/bonding technology for manufacturing of multiplayer engineered substrates.
SOISilicon on Insulator – historically the first commercially significant engineered substrate and now the most common, in which an insulating layer is placed between the front side active layer of silicon where the IC devices are fabricated, and the backside carrier silicon substrate. Applications range from military and space products up to ULSI signal processing ICs.
SubstrateThe starting wafer on which semiconductor devices (“chips”) are built.
TransistorA semiconductor device with more than one positive-negative (p-n) junction, which can either amplify current or voltage, or act as an on-off switch.