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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.

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.

Diamond radiation detectors (DRDs) based on type-IIa chemical vapor deposition (CVD) monocrystal diamond are more suitable for engineering applications with high consistency requirements due to the lower cost and property controllability. However, their saturated charge collection efficiencies (CCEs) have huge differences. Six type-IIa CVD monocrystal diamond plates were analyzed by the Fourier transform infrared spectrometer, high resolution x-ray diffraction, Raman spectroscopy, photoluminescence and secondary ion mass spectroscopy. Then DRDs were fabricated by them and the CCEs were measured under the irradiation of 241Am source. The results show that the most important factor restricting CCEs are the impurities in the diamond plates, while dislocations with a density 7 cm−2 for all samples have weaker impact in our case. The reason is that the carrier mobility-lifetime (μτ) product of diamond is more strongly influenced by impurities in this dislocation density range. Thinning diamond plate, if the thickness is kept above 100 μm, is not a good means to obtain high performance DRDs. Therefore, to further improve the detector performance, ultra-high purity diamond growth is most important. Moreover, a diamond test and selection scheme for high performance DRDs is also demonstrated.

The normally-off hydrogen-terminated diamond metal–semiconductor field effect transistors (MESFETs) with a MoO3 passivation layer were fabricated on the CVD grown polycrystalline diamond substrate. The characteristics of the device at room temperature and 100 °C, 150 °C and 200 °C were investigated. The device with a 2-μm gate shows a threshold voltage of −0.38 V, the maximum output current of 35 mA/mm and the transconductance of 17.4 mS/mm. The device can still work normally until 150 °C, which shows great potential to be used in high temperature in the future.

We report the hydrogen terminated polycrystalline diamond MOSFET with a 10-nm MoO3 gate dielectric and a 50-nm MoO3 passivation layer. The device with a gate length of $2~\mu \text{m}$ shows the saturation drain current ( ${I}_{Dsat})$ of 100mA/mm, the transconductance of 35 mS/mm, and the ON-resistance of $76.54~\Omega \cdot $ mm at ${V}_{GS} = -2.5$ V. The stability of the repeated ${I}_{DS} $ – $ {V}_{GS}$ measurements was demonstrated by a mere ${I}_{Dsat}$ decrease of 3.3% between the first and third sweepings. In addition, the devices worked well at 200 °C delivering even larger ${I}_{Dsat}$ than that at room temperature. The possible mechanisms for ${I}_{DS}$ – $ {V}_{GS}$ changes in the successive measurements and induced by the change of the ambient temperature are suggested.

Hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field effect transistors (MOSFETs) with different structures were fabricated on the same polycrystalline diamond plate and their performances were compared. A 28-nm-thick HfO2 layer grown at 300 °C by atomic layer deposition (ALD) system was used as both gate dielectric and passivation layer. Devices A and B have the same source-to-drain distance of 6 μm but different gate lengths of 2 μm (device A) and 6 μm (device B), and in device B the gate extends over the source/drain electrodes with the HfO2 film separating them. Device C has a similar structure with device A but a larger gate length (6 μm). Among these devices, device A shows the highest saturation drain current of 190.6 mA/mm at VGS = −8 V, and device B shows the lowest on-resistance of 61.61 Ω·mm. All the devices show a high on/off ratio of about 109 and a gate leakage current lower than 10−10 A. It is also extracted a constant carrier mobility of 37.1 cm2/Vs in the gated channel in a large VGS range of −2 V ≤ VGS ≤ −8 V, which indicates the good interface characteristics between H-diamond and HfO2 and contributes to the high device performances. These results indicate that high conductivity 2DHG and high performance MOSFET devices can also be achieved by depositing high temperature grown HfO2 on the H-diamond surface.

We report the performance of a single crystal diamond radiation detector with gold films on hydrogen-terminated diamond as electrical contacts and oxygen-terminated diamond as surface isolation between electrodes. The origin-symmetric current-voltage characteristics showed excellent Ohmic contact behavior. An extremely low dark current value of 7.46 × 10−13 A/mm2 was measured at an electric field of 1 V/μm. The charge collection efficiency and energy resolution of this detector were 99.01% and 1.5% for holes, and 98.6% and 1.7% for electrons under irradiation with 241Am α-particles. Under 60Co γ-ray irradiation with a dose rate of 1.271 Gy/s, the gain factor, specific sensitivities, and signal-to-noise ratio were 49.46, 12.43 μC/Gy·mm3, and 1 × 106 at 200 V bias voltage (0.66 V/μm), respectively. A rise time of 347.4 ps of the response to a pico-second pulsed electron source was also measured. This research provides a possibility to improve the performance of the diamond radiation detector through diamond surface modification.

Hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field effect transistors (MOSFETs) were fabricated on a polycrystalline diamond substrate. The device has a gate length of 2 μm and uses Al2O3 grown by atomic layer deposition at 300 °C as a gate dielectric and passivation layer. The Al2O3/H-diamond interfacial band configuration was investigated by X-ray photoelectron spectroscopy, and a large valence band offset (3.28 eV) that is very suitable for p-channel H-diamond FETs was observed. Meanwhile, the measured O/Al ratio hints that there are Oi or VAl defects in the Al2O3 dielectric, which can work as an acceptorlike transfer doping material on a H-diamond surface. The device delivers the maximum saturation drain current of over 200 mA/mm, which is the highest for 2-μm H-diamond MOSFETs with the gate dielectric or passivation layer grown at 300 °C or higher temperature. The ultrahigh on/off ratio of 1010 and ultralow gate leakage current of below 10−12 A have been achieved. The high device performance is ascribed to the ultrahigh carrier density, good interface characteristics, and device processes. In addition, the transient drain current response of the device can follow the gate voltage switching on/off pulse at a frequency from 100 kHz to 1 MHz, which indicates the potential of the H-diamond FETs in power switch applications.

We report the simultaneous enlarged growth of seven single crystal diamond (SCD) plates free from polycrystalline diamond (PCD) rim by using a microwave plasma chemical vapor deposition (MPCVD) system. Optical microscope and atomic force microscope (AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with (001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum (FWHM) data of both the Raman characteristic peak and (004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.

The single crystal diamond with maximum width about 10 mm has been grown by using microwave plasma chemical vapor deposition equipment. The quality of the grown diamond was characterized using an X-ray diffractometer. The FWHM of the (004) rocking curve is 37.91 arcsec, which is comparable to the result of the electronic grade single crystal diamond commercially obtained from Element Six Ltd. The hydrogen terminated diamond field effect transistors with Au/MoO 3 gates were fabricated based on our CVD diamond and the characteristics of the device were compared with the prototype Al/MoO 3 gate. The device with the Au/MoO 3 gate shows lower on-resistance and higher gate leakage current. The detailed analysis indicates the presence of aluminum oxide at the Al/MoO 3 interface, which has been directly demonstrated by characterizing the interface between Al and MoO 3 by X-ray photoelectron spectroscopy. In addition, there should be a surface transfer doping effect of the MoO 3 layer on H-diamond even with the atmospheric-adsorbate induced 2DHG preserved after MoO 3 deposition.

A MoO3-gated diamond metal–oxide–semiconductor field effect transistor (MOSFET) with a gate length of 40 µm was characterized. Analysis of the flat band voltage shift from the capacitance–voltage hysteresis shows quite high density of the fixed charge presents in the MoO3 layer (1.67 × 1012 cm−2), but the density of the traps brought by MoO3 layer is fairly low (1.35 × 1011 cm−2). The gate voltage dependence of the effective hole mobility was extracted and fitted by the empirical relation widely used in the silicon MOS channel. The resulting low-field mobility without vertical field degradation and the mobility degradation factor are 699 cm2/(Vs) and 1.13, respectively.

Nearly lattice-matched InAlGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08 cm2/Vs together with a high two-dimensional-electron-gas density of 1.43 × 1013 cm−2 for the InAlGaN/GaN heterostructure of 20 nm InAlGaN quaternary barrier. High electron mobility transistors with gate dimensions of 1×50 μm2 and 4 μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.

GaN-based heterostructures with an InAlGaN/AlGaN composite barrier on sapphire (0001) substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAlGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostructures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlGaN quaternary layer is nearly lattice-matched to the GaN channel. Capacitance–voltage results show that there is no parasitic channel formed between the InAlGaN layer and the AlGaN layer. Compared with the InAlGaN/GaN heterostructure, the electrical properties of the InAlGaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm2/V s, 1.44 × 1013 cm−2 and as low as 201.1 ω/sq, respectively.

The epitaxial layers of n-type GaN were grown on both planar and patterned sapphire substrate (PSS) by metal organic chemical vapor deposition. By comparing the epitaxial layers grown on planar substrate, GaN grown on PSS exhibited many improvements both on surface morphology and crystalline quality according to the characterization of atoms force microscopy, and high resolution X-ray diffraction. Spatially resolved micro-Raman scattering results were performed for mapping the spatial variations in crystalline quality of the n-type GaN grown on PSS. According to the variations on the intensity and the full width at half maximum of GaN E2 (high) peaks, the crystalline quality improvement occurred in the lateral growth regions which correspond to center region of the pyramid patterns. We proposed that the bending of dislocations during the lateral growth plays an important role in the spatial variations of GaN crystalline quality. Cross sectional transmission electron microscope and spatial cathodoluminescence mapping results further supported the explanation of the dislocation inhibition during the growth process of GaN grown on PSS.

Epitaxial growth of InAlGaN/GaN structures are performed on the c-plane sapphire by pulsed metal organic chemical vapor deposition with different triethylgallium (TEGa) flows in the growth process of InAlGaN quaternary alloys. X-ray photoelectron spectroscopy results show that the Al/In ratio of the samples increases as the TEGa flows increase in the InAlGaN quaternary growth process. High-resolution x-ray diffraction results show that the crystal quality is improved with increasing TEGa flows. Morphology of the InAlGaN/GaN heterostructures is characterized by an atomic force microscopy, and the growth mode of the InAlGaN quaternary shows a 2D island growth mode. The minimum surface roughness is 0.20 nm with the TEGa flows equaling to 3.6 μmol/min in rms. Hall effect measurement results show that the highest electron mobility μ is 1005.49 cm2 /Vs and the maximal two-dimensional electron gas is 1.63 × 1013 cm−2.

The epitaxial layers of InGaN/GaN MQWs structure were grown on both planar and vicinal sapphire substrates by metal organic chemical vapor deposition. By comparing the epitaxial layers grown on planar substrate, the sample grown on 4° misoriented from c-plane toward < 10 1 ̄ 0 > m-plane substrate exhibited many variations both on surface morphology and optical properties according to the scanning electronic microscopy and cathodoluminescence (CL) spectroscopy results. Many huge steps were observed in the misoriented sample and a large amount of V-shape defects located around the boundary of the steps. Atoms force microscopy images show that the steps were inclined and deep grooves were formed at the boundary of the adjacent steps. Phase separation was observed in the CL spectra. CL mapping results also indicated that the deep grooves could effectively influence the localization of Indium atoms and form an In-rich region.