A semiconductor made from diamond, a crystal of carbon. With a bandgap of about 5.5 eV, one of the highest thermal conductivities of any material and a high breakdown field, it is promising for high-voltage, high-frequency and high-temperature devices, but n-type doping and large substrates are difficult.
Japanese name: ダイヤモンド半導体
Diamond semiconductor appears in 2 practice questions across 1 topic, including Compound semiconductors.
Field: Compound semiconductors
Diamond is an ultra-wide-bandgap semiconductor with a bandgap of about 5.5 eV and an expected breakdown field of about 10 MV/cm, far above the roughly 3 MV/cm of SiC and GaN. Its thermal conductivity of about 2000 W/(m·K) is among the highest of any material, about 5 times that of copper. Electron and hole mobilities are also relatively high, so its theoretical figure of merit for power devices exceeds those of SiC and GaN. For these reasons it is sometimes called the "ultimate semiconductor".
p-type diamond can be made by adding boron, but the acceptor level lies about 0.37 eV above the valence band, so only part of the boron releases holes at room temperature. n-type is even harder: the phosphorus donor level is about 0.57 eV below the conduction band, so very few electrons are free at room temperature. The lack of shallow levels from which nearly all dopants release carriers, as in Si or SiC, is the fundamental reason diamond devices are difficult.
When a diamond surface is terminated with hydrogen atoms, a thin conducting layer of holes (a two-dimensional hole gas) forms just below it. It is thought to arise from electron exchange with substances adsorbed on the surface, and adsorbing NO2 or similar molecules raises the hole density. Because this avoids the problem of deep dopant levels, p-channel MOSFETs using the surface layer as the channel are being researched. In 2023 Saga University announced the operation of a power circuit using p-channel diamond MOSFETs with holes induced by NO2.
Single-crystal diamond is made by methods such as CVD (chemical vapor deposition) from methane and hydrogen, but inexpensive mass production of large-diameter, low-defect substrates like those for Si or SiC is still difficult, so research as of the mid-2020s centers on small substrates. Besides high-voltage power devices, applications under study include high-frequency high-power amplifiers, devices tolerant of radiation and high temperature, and quantum sensors using nitrogen-vacancy (NV) centers in diamond.
Answer: B. The phosphorus donor level lies about 0.57 eV below the conduction band, so it hardly ionizes at room temperature
For a donor to release an electron, the electron must be thermally lifted from the donor level to the conduction band. In silicon the phosphorus level is shallow, about 0.045 eV below the conduction band, so nearly all of it ionizes at room temperature. In a diamond semiconductor the phosphorus level is deep at about 0.57 eV, far more than the room-temperature thermal energy (about 0.026 eV), so most phosphorus atoms release no electrons. The boron acceptor is also fairly deep at about 0.37 eV, making doping a major challenge in diamond device development.
Answer: A. A thin layer of holes forms just below the surface, allowing p-channel transistors that avoid the problem of deep dopant levels
In a diamond semiconductor, boron and phosphorus levels are deep, so it is hard to obtain enough carriers at room temperature. When the surface is hydrogen-terminated, electron exchange with adsorbed substances forms a two-dimensional hole gas just below the surface. Adsorbing NO2 or similar molecules raises the hole density, and p-channel MOSFETs using this layer as the channel are being studied. In 2023 Saga University announced the operation of a power circuit using diamond MOSFETs with holes induced by NO2.
It combines a large bandgap of about 5.5 eV, a high breakdown field of about 10 MV/cm and one of the highest thermal conductivities of any material. It is expected to suit high-voltage power devices that generate much heat and devices used at high temperature or under radiation.
The phosphorus donor level lies about 0.57 eV below the conduction band, so it releases almost no electrons at room temperature. The boron acceptor is also fairly deep at about 0.37 eV, so low room-temperature carrier density is a common problem.
As of the mid-2020s it is in research and development. Results such as working power circuits have been reported, but mass production of large, high-quality substrates and solving the doping problem are key to practical use.
In a diamond semiconductor the phosphorus level is deep at about 0.57 eV, far more than the room-temperature thermal energy (about 0.026 eV), so most phosphorus atoms release no electrons.
In a diamond semiconductor, why is the room-temperature ele…In a diamond semiconductor, boron and phosphorus levels are deep, so it is hard to obtain enough carriers at room temperature.
Why is the conducting layer formed by hydrogen-terminating …As an Amazon Associate I earn from qualifying purchases.
Donor Acceptor 2DEG (two-dimensional electron gas) Alloy semiconductor Direct band gap Efficiency droop Ga2O3 (gallium oxide) GaAs (gallium arsenide) GaN (gallium nitride) HEMT (high-electron-mobility transistor)