High Power Microwave Plasma Chemical Vapor Deposition Research Articles

Characterization of diamond ultraviolet detectors fabricated with high-quality single-crystalline chemical vapor deposition films

We have fabricated high-performance ultraviolet (UV) detectors with high-quality undoped and B-doped homoepitaxial diamond layers which were sequentially grown on a high-pressure/high-temperature-synthesized (HPHT) type-Ib (100) substrate by means of a high-power microwave-plasma chemical vapor deposition method. The detector performance measured had large quantum efficiencies due to an effective built-in current amplification function, fast temporal responses, and high UV/visible sensing ratios although the HPHT substrate used had considerable amounts of various defects inducing visible light absorptions and slow detector responses. The usefulness of the bilayer detector structure employed is discussed.

Highly efficient doping of boron into high-quality homoepitaxial diamond films

High-quality boron-doped homoepitaxial diamond (100) films were grown using high-power microwave plasma chemical vapor deposition (MPCVD). Results showed that the incorporation efficiency of boron from gas phase was increased by two orders of magnitude compared to those of conventional growth conditions using high-density plasma. Boron-doped crystal thus grown with the low B / C ratio of 50 ppm in the gas phase had reasonably low resistivity of 2 Ω cm at 290 K, whereas Hall mobility of 830 cm 2 V s − 1 at this temperature was higher than those reported previous for such resistivity. The highly boron-doped film showed strong free exciton recombination emissions with a bound exciton component in the cathodoluminescence spectra taken at room temperature, reflecting the considerably high density of the substitutional boron in the film despite its low density of electronic defects. The diamond growth rate in the high-power MPCVD was 3.5 μm h − 1 . The highest room-temperature Hall mobility achieved in this study was 1620 cm 2 V s − 1 . These results indicate that the resultant high-rate growth with high-power MPCVD is advantageous for depositing high-quality and conductive diamond films.

High-quality homoepitaxial diamond (100) films grown under high-rate growth condition

We present advantages of high-power microwave plasma chemical vapor deposition (MPCVD) in homoepitaxial diamond film deposition. Diamond films grown at comparatively high growth rate of 3.5 μm/h showed intense free-exciton recombination emission at room temperature. The free-exciton decay time of the diamond film at room temperature, 22 ns, was much longer than that of type-IIa single crystal, indicating electronically high quality of the homoepitaxial films. Dislocation-related emissions were locally observed, a part of which created by mechanical polishing process was successfully removed by surface etching process using oxygen plasma. Another advantage of the high-power MPCVD is effective impurity doping; boron-doped diamond films with high carrier mobility and high carrier concentration were reproducibly deposited. An ultraviolet photodetector fabricated using the high-quality undoped diamond film showed lower noise equivalent power as well as higher photoresponsivity for ultraviolet light with better visible-blind property, compared to those of standard Si-based photodetectors. The high-power MPCVD is, thus, indispensable technique for depositing high quality diamond films for electronic devices.

High rate growth and electrical/optical properties of high-quality homoepitaxial diamond (100) films

Undoped and boron doped homoepitaxial diamond films were grown by high-power microwave plasma chemical vapor deposition (MPCVD). Growth rate was 2.5 μm/h under optimized growth conditions. The grown undoped film thus grown showed large diffusion length of 10.2 μm while short lifetime of 15 ns for electron. The growth rate increased up to 25 μm/h with increasing methane concentration, while free-exciton recombination emission was observed at room temperature. We found the surface became smooth and growth rate increased with increasing substrate temperature. Hall measurement for boron-doped sample revealed high hole mobility of 1500 cm 2/Vs at 290 K for relatively high acceptor density of 1.4×10 18 cm –3. The high-power MPCVD is, thus, indispensable for high-rate growth of diamond films for electronic devices.

Transport properties of electron-beam and photo excited carriers in high-quality single-crystalline chemical-vapor-deposition diamond films

We have investigated transport properties of carriers excited in high-quality homoepitaxial diamond (100) films by 5.6eV photons or 15keV electrons. The high-quality single-crystalline diamond films were homoepitaxially grown on type-Ib diamond substrates at a rate of 2.5μm∕h by high-power microwave-plasma chemical-vapor-deposition (MPCVD). In cathodoluminescence (CL) measurements, strong free-exciton recombination emissions were observed at room temperature from the almost whole specimen surface, indicating the grown films have substantially high quality. It is found through an analysis of the visible emission band originating from the type-Ib substrate that decay constants estimated for excited carriers were ∼5μm in the depth direction. This is consistent with the fact that the intensity of spotlike CL images varied with an exponential function of the lateral length. From transient photocurrent measurements using ultrashort pulse laser excitations, decay times τ for the present high-quality diamond were estimated to be 15 and 100ns for electrons and holes, respectively. Charge collection distances at an electric field E of 830V∕cm were deduced to be ∼190μm and over 1.2mm for electrons and holes, respectively. The former may give a high electron drift mobility of μ∼1600cm2∕Vs while the diffusion coefficients estimated for electrons are 55±14cm2∕Vs, which is comparable with or even higher than those of Si. These physical quantities demonstrate high quality of the diamond films grown by means of the high-power MPCVD method.

High-quality boron-doped homoepitaxial diamond grown by high-power microwave-plasma chemical-vapor deposition

Boron-doped homoepitaxial diamond (100) films with substantially flat surface have been deposited by a high-power microwave-plasma chemical-vapor-deposition (MPCVD) method. Hall mobilities of 1500cm2∕Vs at 290K and 2220cm2∕Vs at 235K were attained for such a specimen with an acceptor density of 1.4×1018cm−3 grown at a growth rate of 3.5μm∕h. These mobilities are comparable with those of the highest quality homoepitaxial diamond grown by a standard low-power MPCVD method, where the growth rate and carrier concentration were, respectively, ∼1∕30 and 1∕5 of the corresponding values attained in the present case. This fact verifies that the high-power MPCVD is suitable for deposition of a high quality and high carrier-concentration p-type diamond at a reasonably high growth rate.

Homoepitaxial diamond growth by high-power microwave-plasma chemical vapor deposition

We have investigated homoepitaxial diamond growth by high-power microwave-plasma chemical-vapor-deposition (MPCVD) method. The diamond growth rate R g increased linearly with increase in the methane flow-rate ratio in the total source gas flow, C me , only for C me > 4 % while increasing non-linearly with the C me for C me < 4.0 % under the high microwave power condition of 3.8 kW. In the case of the present high-power MPCVD, saturation of R g, that often occurred at C me ≈ 1.0 % in conventional MPCVD cases, was not observed in the whole C me range examined (⩽32%). The crystalline quality of diamond films became relatively better and the surface morphology became smooth without non-epitaxial crystallites in the C me range from 4.0 to 8.0% under the growth conditions. For R g > 10 μm/h, however, formation of round-shape hillocks, various defects and vacancies including nitrogen-related CL centers occurred in some cases. It is found that these degradations, which occurred for C me > 10.0 % in the present MPCVD case, can be suppressed by increasing plasma density using higher microwave power of 4.7 kW and higher total gas pressure of 160 Torr. Possible reasons for the observed advantages in the present high-power MPCVD method are discussed.

Highly efficient electron emitting diode fabricated with single-crystalline diamond

Abstract Highly efficient electron emitting diodes have successfully been fabricated using single-crystalline diamond films epitaxially grown on high-pressure synthesized (100) diamond. It turns out that the crystalline quality of the diamond used is essential to the present-type electron emitter operated under extremely high electric fields of ∼107 V/cm. For the electron emitting diode, the current efficiency defined as the ratio of the emission current to the driving current can reach unity in the best case. The mechanism of the highly efficient electron emission observed is discussed in relation to possible carrier excitations in the undoped diamond layer under the high fields. Using a high-power microwave-plasma chemical vapor deposition apparatus, high-quality diamond thin films were homoepitaxially grown. It is found from measuring the threshold energy of total photoelectron yields that a moderate surface oxidation process can change the surface electric dipole layer and, therefore, the electron affinity for hydrogen-terminated diamond surfaces as the Topping model shows.