Kyma offers two basic types of substrates: bulk substrates and templates. The term bulk substrate refers to a free-standing substrate such as bulk gallium nitride (GaN) substrates which Kyma provides. Other bulk substrates provided by others in the industry include sapphire, silicon, gallium arsenide (GaAs), indium phosphide (InP), etc. Bulk substrates are usually single crystal in nature, although polycrystalline bulk gallium nitride (GaN) substrates are also available from Kyma.
The term template refers to a thin layer of a crystalline material deposited on an otherwise bulk substrate. Kyma offers aluminum nitride (AlN) on sapphire templates, aluminum nitride (AlN) on silicon templates, gallium nitride (GaN) on sapphire, gallium nitride (GaN) on silicon, and aluminum gallium nitride (AlGaN) on sapphire.
Wide-bandgap semiconductors (WBG or WBGS) area a class of semiconductors which have risen in popularity for more targeted electronic and optoelectronic applications such as power electronics, radio frequency (RF) applications, and visible to ultraviolet LEDs and lasers. These materials have bandgaps which are 2 eV or greater, which are larger than conventional semiconductors such as silicon or other III-V semiconductors. Semiconductors in the WBG category include gallium nitride (GaN), silicon carbide (SiC), and more.
Ultra-wide bandgap semiconductor (UWBGS) materials are a subset of WBGS materials and are defined as those WBGS materials which have a bandgap above that of GaN, which is 3.4 eV. This includes materials such as diamond, gallium oxide (Ga2O3), AlGaN, and AlN. UWBGS materials have the potential to support the realization of devices with even higher levels of performance than devices based on Si, GaAs, SiC, or GaN.
Gallium oxide, especially in its beta-form, is an exciting ultra-wide bandgap semiconductor (UWBGS) material due to its tantalizing mix of physical properties that together translate to very high figures of merit for a number of high speed electronics and power electronics applications. However, most such figures of merit don't include a thermal conductivity term and that is where Ga2O3 has limitations - it has a very low thermal conductivity when compared to other WBGS materials. A big plus however is that diameter-scalable processes exist for making bulk Ga2O3 substrates which in turn enables homoepitaxial Ga2O3 devices to be fabricated. In contrast, because high quality GaN substrates are still in short supply, most GaN devices are made on non-GaN substrates, leading to high defect densities in the GaN epilayers. Also, beta-Ga2O3 has a direct bandgap, and, because it can be alloyed with Al and In one can imagine interesting (Al,Ga)2O3/(In,Ga)2O3 heterostructures for future electronic and optoelectronic device applications.
A photoconductive semiconductor switch, or PCSS, is a device concept based on a semiconductor material that conducts electricity when it is turned on with light. Before the light turns it on, it does not conduct electricity. In most types of PCSS devices, the electrical conduction ceases or rapidly decays once the light source is turned off. In other cases the electrical conduction might continue, which is called a "latch-on" effect.There are many applications for PCSS devices, some which benefit from a fast turn-on and/or turn-off response times and others that benefit from a slow turn-on and/or turn-off response times.A major benefit of GaN and other wide bandgap semiconductors for PCSS applications is the potential for high voltage and high power switching. Indeed, Kyma's KO-Switch™ is the highest voltage and fastest GaN PCSS device on the market, we believe.Such benefits and many more details about PCSS devices are described nicely in a recently published article called "Wide Bandgap Extrinsic Photoconductive Switches" by J.S. Sullivan of Lawrence Livermore National Laboratory (LLNL) - that report is publicly available and can be downloaded at https://e-reports-ext.llnl.gov/pdf/759551.pdf.Kyma's published "High Voltage Bulk GaN-Based Photoconductive Switches for Pulsed Power Applications" is also available to the public and can be downloaded on the SPIE website.
Kyma's name is based on the Greek word "κύμα" which means wave in English. The pronunciation of Kyma is like "keema" although many pronounce our company name like "kima" - we are fine with either. Most of Kyma's products are used to improve the cost and performance of optoelectronic and electronic semiconductor devices such as LEDs, laser diodes, Schottky diodes, and transistors and acoustic wave devices too. Kyma's name refers to the wave-like properties of electrons, holes, phonons, and photons, which are the active species in these devices.
The term "engineered substrate" has different meanings depending on the context. For semiconductor device manufacturing it usually refers to a special type of substrate upon which epitaxy is carried out to create a device epiwafer. The special type in this case is that it is neither a bulk or free-standing substrate such as GaN or SiC or sapphire, nor is it a simple template substrate such as that of a GaN on sapphire template. One example of an engineered substrate is that of a thin crystalline layer of GaAs, InP, or GaN that is bonded on top of a silicon, sapphire, ceramic, or metal substrate. Considerations into engineered substrate design includes that the base material may be chosen for its physical properties (diameter, thermal expansion coefficient, thermal conductivity) and low cost while the upper region may be chosen primarily for its ability to support high quality epitaxy.
