Frequently asked questions

What are the basic differences between a "bulk substrate" and a "template"

Kyma offers two basic types of substrates: bulk substrates and templates.The term bulk substrate refers to a free-standing substrate such as bulk GaN substrates which Kyma provides. Other bulk substrates provided by others in the industry include Sapphire, Si, GaAs, InP, etc. Bulk substrates are usually single crystal in nature, although polycrystalline bulk 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 AlN on sapphire templates, AlN on SI templates, GaN on sapphire, GaN on Si, and AlGaN on sapphire. Most, but not all, of Kyma's template customers provide us with the underlying substrate. For example, most of our AlN on sapphire template customers send us their sapphire and we deposit the AlN and ship it back to the customer.

What is the story behind Kyma's name

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.

What is a photoconductive semiconductor switch (PCSS)

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'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.

What is a transition metal dichalcogenide (TMD)

Transition metal dichalcogenide (TMD) monolayers are atomically thin semiconductors of the type MX2, with M a transition metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, etc.). One layer of M atoms is sandwiched between two layers of X atoms. For example, a MoS2 monolayer is 6.5 Å thick.The discovery of graphene shows how new physical properties emerge when a bulk crystal of macroscopic dimensions is thinned down to one atomic layer. Like graphite, TMD bulk crystals are formed of monolayers bound to each other by Van-der-Waals attraction. TMD monolayers have properties that are distinctly different from those of the semimetal grahene.

What is the thermal conductivity of Gallium Nitride(GaN)

Thermal conductivity (TC) is a measure of the ability of a material to conduct heat and it is expressed in units of energy per unit distance per unit temperature. For non-metallic crystalline materials including gallium nitride (GaN), heat is conducted mostly through lattice vibrations (phonons). Therefore, the thermal conductivity can be reduced by anything that affects phonon physics, which includes dislocations and other extended defects, intrinsic point defects such as vacancies and antisites, and extrinsic defects (impurities). And because phonon activity is temperature dependent, TC varies with temperature as well. For these reasons, room temperature TC of GaN varies from ~100 W/m·K for highly defective GaN epilayers grown on Si and sapphire to 165 W/m·K for Kyma's polycrystalline GaN to 260 W/m·K for Kyma's bulk GaN. See Kyma's 2011 press release for additional information.

What is a engineered substrate

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.

What is an ultra-wide bandgap semiconductor (uwbgs) material

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.

What is a wide bandgap semiconductor (wbgs) material

According to Wikipedia: Wide-bandgap semiconductors (WBG or WBGS) are semiconductor materials that permit devices to operate at much higher voltages, frequencies and temperatures than conventional semiconductor materials like silicon and gallium arsenide. They are the key component used to make green and blue LEDs and lasers, and are also used in certain radio frequency applications, notably military radars. Their inherent qualities make them suitable for a wide range of roles, and they are one of the leading contenders for next-generation devices for general semiconductor use. "Wide-bandgap" refers to higher-energy electronic band gaps, the difference in energy levels that creates the semiconductor action as electrons switch between the two levels. Silicon and other common non-wide-bandgap materials have a bandgap on the order of 1 to 1.5 electronvolt (eV). Wide-bandgap materials in contrast typically have bandgaps on the order of 2 to 4 eV.While Wikipedia introduces the concept well, please note that 4 eV is not the limit of bandgap energies, as diamond has a bandgap of 5.5 eV and the beta phase of gallium oxide (Ga2O3) has a bandgap of 4.85 eV.

What are scientists doing to make larger area diamond wafers

Diamond is a semiconductor material with a very large bandgap of 5.5eV and thus falls into both categories of wide bandgap semiconductor (WBGS) and ultra-WBGS (UWBGS). Because of its physical properties it has great promise to enable higher performance electronic devices. Much progress has been made in the manufacturing of diamond crystals, leading to lower cost diamond materials that are superior to naturally occurring diamonds in terms of crystallinity and chemical purity. Yet for diamond electronics to really take off, large area high quality diamond wafers are needed - at least 2" in diameter and preferably 6" (150 mm) or 8" (200 mm). Therefore there is research going on world-wide seeking to increase the size of single crystal "electronic grade" diamond wafers. Several approaches are being investigated to make large area high quality diamond wafers. One approach is to arrange small high quality diamond wafers side-by-side and then deposit diamond on both the top and the bottom. This process is also called "stitching" and has created the largest area single crystal diamond wafers so far. Another approach is to grow on the top of a small diamond crystal, then turn it on its side, grow some more, then turn it again and repeat - hoping to produce a large diamond boule from which large area diamond wafers can be sliced. This is a very slow and costly approach. Another approach is use a vapor phase process to grow large area diamond right away (e.g., on a 4" silicon wafer) - this works fairly well except that it results in polycrystalline damond and not the high quality single crystal form needed for proper electronic device manufacturing.

Why is gallium oxide (GA2O3) getting so much attention

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.

What are the primary variants of graphene and graphite

Much of the following is derived from Wikipedia plus a nice multi-year discussion on Research Gate and we also add some comments on stability and packaging to try to make for a clearer picture:    a) Graphene is an allotrope (form) of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice.    b) Graphene oxide (GO) is an oxydized form of graphene and is the single-layer form of graphite - we are hoping GO will get its own Wikipedia page - seems one has been started here. Our partners at GOLeafe Inc. helped us understand that GO is somewhat unstable as it will convert reduced graphene oxide (rGO - see below) when subjected to heat or light. So when we ship GO we make sure it is from a fresh batch and we use a proper container to keep light out. GO is relatively soluble in water.    c) Reduced graphene oxide (rGO) is a less than full oxidized form of graphene oxide. It is relatively stable and thus has a long shelf life. rGO is less soluble in water than GO.All of the above (graphene, GO, and rGO) can exist in single monolayer form and they can also be stacked to form bilayers, trilayers, etc.All of the below (graphite oxide and graphite) are bulk materials which can be less expensive to make than monolayer materials but which are much less interesting for a large range of applications.    
d) Graphite oxide, formerly called graphitic oxide or graphitic acid, is a compound of carbon, oxygen, and hydrogen in variable ratios, obtained by treating graphite with strong oxidizers.    
e) Graphite, archaically referred to as plumbago, is a crystalline allotrope of carbon, a semimetal, a native element mineral, and a form of coal.

Where are some available discussions of graphene markets & applications

The Market for Graphene and related materials are discussed here, here, and here.Overall Applications for Graphene and related materials are discussed here and here.Clean Energy applications for graphene and related materials are discussed here and here.Battery applications of graphene and related materials are discussed here, here, and here.Desalination applications of graphene and related materials are discussed here and here.

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