Search for: All records

Diamond electronics has attracted attention for high power and high frequency device applications. Cubic boron nitride (c-BN) may be considered as a suitable dielectric layer for electron channel diamond metal–insulator–semiconductor field effect transistors (MISFETs) provided that its valence band edge can be positioned above that of diamond. This study reports experimental measurement of the valence band offset (VBO) between c-BN and nitrogen-plasma terminated boron-doped diamond (111). Nitrogen plasma processing was used to produce C–N bonding at the diamond surface. Electron cyclotron resonance plasma enhanced chemical vapor deposition was then used to deposit epitaxial c-BN films on the N-terminated diamond substrate, as confirmed by cross-sectional high-resolution electron microscopy. X-ray and ultraviolet photoemission spectroscopies indicated that the valence band maximum of c-BN is positioned 0.4 eV above that of diamond resulting in a type II staggered band alignment. This result is consistent with theoretical predictions of the VBO between the two materials in the (111) surface orientation, indicating that c-BN with C–N interface bonding can be used as a dielectric layer for electron channel diamond (111) MISFET devices. 

Various reports on phosphorus‐doped diamond growth present a prominent variation in the doping profile and the doping gradient at the substrate/epilayer interface. This warrants a closer investigation of the growth process, in particular, the gas chemistry via residual gas analysis (RGA) to determine whether a doping indicator exists that would allow a real‐time control of the phosphorus incorporation. Phosphorus‐doped diamond films are prepared by plasma‐enhanced chemical vapor deposition utilizing a 200 ppm trimethylphosphine in hydrogen gas mixture. The phosphorus‐doped diamond growth is characterized by in situ RGA, which identifies a diatomic radical (PH) formed in the hydrogen plasma. A rapid analysis response is achieved through an engineered differentially pumped component. Secondary ion mass spectroscopy (SIMS) is employed to evaluate the phosphorus incorporation in the doped diamond epilayers. The SIMS‐derived phosphorus doping profile is correlated to the RGA‐measured PH concentration. For an epilayer grown on a (111) chemical vapor deposition‐type IIa substrate with moderate miscut a significant phosphorus incorporation of 4.5 × 10¹⁹ cm⁻³is measured with an incorporation efficiency of about 10%. A doping model is derived that utilizes RGA for dominant growth and doping species and under consideration of various growth modes. 

Epitaxial films of cubic boron nitride (c-BN) have been grown on single-crystal boron-doped diamond substrates by electron cyclotron resonance plasma-enhanced chemical vapor deposition using gas mixtures of Ar–He–N2–BF3–H2. The resulting c-BN films have been characterized using in situ x-ray photoelectron spectroscopy to establish the growth surface bonding (i.e., sp3 or sp2). The interface and film crystal structure were characterized with high resolution electron microscopy and electron-energy-loss spectroscopy. This study considers three stages of the growth process: in situ surface preparation, initial nucleation and growth of c-BN, and growth of the epitaxial c-BN layer. Prior studies from our group have established that hydrogen gas phase concentration affects fluorine-induced etching and c-BN nucleation. The results of this study establish that by optimizing the surface chemistry for all three stages of the growth process, it is possible to achieve an adherent, oriented epitaxial c-BN layer, a workable growth rate (∼50 nm/hr), cubic phase BN throughout, and negligible sp2 bonding except at the interface. 

Cubic boron nitride (c-BN), with a small 1.4% lattice mismatch with diamond, presents a heterostructure with multiple opportunities for electronic device applications. However, the formation of c-BN/diamond heterostructures has been limited by the tendency to form hexagonal BN at the interface. In this study, c-BN has been deposited on free standing polycrystalline and single crystal boron-doped diamond substrates via electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD), employing fluorine chemistry. In situ x-ray photoelectron spectroscopy (XPS) is used to characterize the nucleation and growth of boron nitride (BN) films as a function of hydrogen gas flow rates during deposition. The PECVD growth rate of BN was found to increase with increased hydrogen gas flow. In the absence of hydrogen gas flow, the BN layer was reduced in thickness or etched. The XPS results show that an excess of hydrogen gas significantly increases the percent of sp2 bonding, characteristic of hexagonal BN (h-BN), particularly during initial layer growth. Reducing the hydrogen flow, such that hydrogen gas is the limiting reactant, minimizes the sp2 bonding during the nucleation of BN. TEM results indicate the partial coverage of the diamond with thin epitaxial islands of c-BN. The limited hydrogen reaction is found to be a favorable growth environment for c-BN on boron-doped diamond. 

A thin layer of Al 2 O 3 was employed as an interfacial layer between surface conductive hydrogen-terminated (H-terminated) diamond and MoO 3 to increase the distance between the hole accumulation layer in diamond and negatively charged states in the acceptor layer and, thus, reduce the Coulomb scattering and increase the hole mobility. The valence band offsets are found to be 2.7 and 3.1 eV for Al 2 O 3 /H-terminated diamond and MoO 3 /H-terminated diamond, respectively. Compared to the MoO 3 /H-terminated diamond structure, a higher hole mobility was achieved with Al 2 O 3 inserted as an interface layer. This work provides a strategy to achieve increased hole mobility of surface conductive diamond by using optimal interlayer along with high high electron affinity surface acceptor materials.