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Multiple-channel GaN heterostructures have been used to improve the device performance of high electron mobility transistors (HEMTs). The object is to achieve highly linear transconductance, low ON-resistance, and large output current. However, the complicated situation of the multiple channels made it difficult to model multiple-channel HEMTs. We report an analytical model of the electron population and the energy band diagram of multiple-channel GaN heterostructures. It is established based on the continuity of electric displacement vector at various interfaces and the electric neutrality of the whole heterostructure. The double-channel, triple-channel, four-channel, and ten-channel heterostructures have been investigated, and the calculation results are compared with the numerical self-consistent Schrodinger–Poisson solution to show the feasibility of the model.

C-H diamond metal-oxide-semiconductor field effect transistors with different structures were fabricated on the same polycrystalline diamond plate. Devices A and B with 25-nm-thick high temperature (300°C) atomic layer deposition grown Al2O3 dielectric have the same source-to-drain distance of $6~\mu \text{m}$ and different gate length of $2~\mu \text{m}$ and $6~\mu \text{m}$ , respectively. Both devices show ultra-high on/off ratio of over 1010 and ultra-low gate leakage of below 10−10 A and continuous measurement stability. Device B with the source/drain-channel interspaces eliminated has achieved an on resistance of $46.20~\Omega \cdot $ mm, which is record low in the reported 6- $\mu \text{m}$ H-diamond MOSFETs with the gate dielectric prepared at high temperature (≥ 300°C). Meanwhile, device B shows larger drain current in a large portion of the linear region at VGS = −6 V, and a just slightly smaller IDmax compared with device A though its LG is three times of that of device A. A simple model of ID was used to explain the physics behind this phenomenon. In addition, the breakdown voltage is 145 V for device A and 27 V for device B, corresponding to the average breakdown field of about 0.72 MV/cm and 10.8 MV/cm, respectively.

A hydrogen-terminated diamond (H-diamond) Field effect transistor (FET) with a ferroelectric HfZrOx/Al2O3 stacked gate dielectric was demonstrated for the first time. The HfZrOx(16 nm)/Al2O3(4 nm) gate dielectric was grown by atomic layer deposition (ALD) at 300 °C. The bowknot-like capacitance-voltage hysteresis and the transfer characteristic curves in clockwise hysteresis loop directly illustrated the ferroelectricity of the device. A memory window as wide as 7.3-9.2 V, the maximum on/off ratio of 109 and the subthreshold slope (SS) of about 58 mV/decade was measured for the gate voltage sweeping between 10.0 to -10.0 V in the linear region. A completely normally-off behavior was observed in the saturation region because both threshold voltages (Vth 's) for forward and reverse sweeping transfer characteristic curves are negative at a drain voltage of -15 V. It is ascribed to that the polarization state of the HfZrOx dielectric along the channel changes from uniform in the linear region to strongly nonuniform in the saturation region. These results hint that HfZrOx/Al2O3/H-diamond FETs provide new possibility of diamond normally-off FETs, negative capacitance FETs and non-volatile memory of high density integration.

High performance normally-off hydrogen-terminated diamond (H-diamond) MOSFETs were fabricated on single crystalline diamond grown in our lab. The device with 2- $\mu \text{m}$ gate length shows threshold voltage of −1.0 V, and a drain current of 51.6 mA/mm at $V_{\mathrm{ GS}}= {V}_{\mathrm{ DS}} = -4.5$ V and an on-resistance of $65.39~ \Omega \cdot $ mm. The transconductance keeps increasing when $\text{V}_{\mathrm{ GS}}$ shifts from $\text{V}_{\mathrm{ TH}}$ toward more negative direction, and reaches the record high value of 20 mS/mm at $\text{V}_{\mathrm{ GS}}$ of −4.5 V, which benefitted from the almost constant mobility of the holes in the gate voltage range of −4 V $ V. The critical device process to realize these low on-resistance normally-off MOSFETs consists of 2-min UV ozone treatment of the H-diamond surface and thermal oxidation of aluminum film in the air to form an alumina gate dielectric.

Among the known color centers of diamond, the nitrogen-vacancy (NV) center composed of a substitutional nitrogen and its nearest carbon vacancy could be the most promising photon emitter. In this work, we present the micro-photoluminescence (μ-PL) landscapes of two quasi-localized vibrational resonances (∼45 and ∼63 meV) associated with the neutral (NV0) and negative (NV−) NV centers, respectively. A symmetric electron–phonon coupling theoretical model was used to simulate the μ-PL spectra with vibronic structures, so that the effective phonon densities of states and Huang–Rhys factors could be obtained for the two charge states of the NV centers. Our study also reveals that the perfect lattice optical phonon mode plays a more significant role in the luminescence of the NV0 state, whereas the quasi-localized vibrational resonance plays the dominant role in the case of NV−. These new results may deepen the existing understanding of the luminescence properties of the NV centers in diamond.

We report a normally-off C H diamond metal-insulator-semiconductor field effect transistor (MISFET) using a 15-nm-thick thermally evaporated MgF2 film as both the gate dielectric and the passivation layer. The normally-off channel is directly formed based on the Al/MgF2/C-H diamond MIS gate structure. The 4-μm device delivers a record high transconductance (gm) of 26.2 mS/mm among normally-off C H diamond FETs, and a threshold voltage of −0.60 V, a maximum μeff of 138.9 cm2/V·s, a maximum drain current (IDmax) of −49.7 mA/mm and an on-resistance (Ron) of 84.4 Ω·mm at the gate voltage of −5 V. The low Ron and high gm and large IDmax arise from the good conductivity at the MgF2/C-H diamond interface, and the normally-off operation could be attributed to the depletion effect of the gate on the channel with its 2DHG conductivity just slightly degraded after MgF2 deposition.

The hydrogen terminated diamond (H-diamond) field effect transistors (FETs) have been the mainstream structure of diamond microwave power devices, but to improve their performance is still very challenging. A detailed analysis of the microwave power performance at 1GHz of a 0.5-μm H-diamond FET with 25-nm-thick Al2O3 gate insulator is carried out by numerical simulation of the large signal transients, and a GaN high electron mobility transistors (HEMT) in similar structure is used as a reference. Compared with the output power (Pout) of 10.76 W/mm demonstrated at a quiescent drain bias (VdQ = 48 V) by the GaN HEMT, the H-diamond FET achieved about one third of Pout (3.69 W/mm) at VdQ = -57 V based on the transconductance with much lower peak intensity (less than one fifth) but better linearity. According to the location of the dynamic load line on the direct current output characteristics, the available drain current swing has been fully utilized in the H-diamond FET. Further Pout improvement need higher bias point and larger dynamic swing of the drain voltage.

The nitrogen–vacancy (NV) center in diamond has quickly emerged as a promising solid–state candidate for single-photon emitters, quantum bits or qubits, and ultrasensitive sensors in recent years. At the same time, it may also provide an excellent molecule–like platform for exploiting the fundamental principles of quantum mechanics, such as quantum entanglement mechanism. Therefore, it is of both scientific and technological significance to have an in-depth investigation on NV center, especially on the optoelectronic processes and optical properties of NV center. In this study, the temperature dependence of the sharp zero–phonon lines (ZPL) of luminescence of NV center with neutral and negative charge states in a CVD–grown diamond crystal is measured in the range from 5 K to 300 K. It is shown that the experimental data, including the temperature induced broadening, peak shift and even intensity quenching of the two sharp ZPL lines of NV0 and NV−1, all on the whole support a generalized quantum theory in spite of in which Franck–Condon, harmonic and Debye approximations were assumed. In particular, the thermal quenching tendency of the integrated intensities can be described by Debye–Waller factor in the theory of the Mossbauer effect. The study sheds some light on the challenging issue, the temperature dependence of the so–called zero-phonon luminescence of NV center in diamond.

We report the first attempt of the diamond MOSFETs with MoO3 dielectric directly deposited on H-diamond surface preserving atmospheric-adsorbate-induced 2DHG. The transistors with 4- $\mu \text{m}$ gate show a transconductance of 29 mS/mm and an ON-resistance of $75.25~\Omega \cdot \text {mm}$ at $\vert V_{\text {GS}} - V_{\text {TH}}\vert = 2.2$ V, respectively. The effective mobility is extracted to be 108 cm2/(Vs) from the relationship between the ON-resistance and $\vert V_{\text {GS}}- V_{\text {TH}}\vert $ . The relatively high transconductance among the reported diamond MOSFETs with the same gate length could be attributed to the quite low ON-resistance. The evaluated high mobility indicates good interface characteristics between diamond and MoO3. However, the saturation drain current is limited at 33 mA/mm by the forward gate breakdown at $\text{V}_{\text {GS}}$ of around −2 V.