Excitonic emission and N‐ and B‐incorporation in homoepitaxial CVD‐grown diamond investigated by cathodoluminescence

Abstract

Diamond is a very large bandgap material arising high expectations either for optoelectronic applications or for active semiconducting layers in specific electronic devices to be used under extreme conditions of pressure, temperature, wear or radiation, as well as in chemically aggressive environments. Unintentionally boron-doped diamond layers were grown by microwave plasma-assisted chemical vapour deposition (CVD) on {001}-oriented undoped Ib substrates with the addition of oxygen gas during growth. The relative quantities of nitrogen and boron incorporated in the diamond lattice are evaluated by cathodoluminescence (CL) spectra recorded at 5 K. Two different effects are shown to limit nitrogen incorporation: the substrate crystalline quality and the addition of oxygen into the precursor during the growth. First, the CL spectra are shown to change strongly near the edges of the substrate in the regions corresponding to different bulk crystal growth modes. Some regions show a luminescence governed by UV emission while in other regions, where the H3 defect-related luminescence of the substrate is much stronger, the film UV emission is reduced. Second, the relative importance of the free exciton emission with respect to those from the nitrogen-related H3 centre and from the boron-bound exciton is shown to increase with the addition of oxygen during growth. Such observations are of first importance to improve the spectral emission and absorption threshold of the diamond material in the deep UV range.

Hydrogen passivation of boron acceptors in as-grown boron-doped CVD diamond epilayers

“…Indeed, the ratio between intensity peaks attributed to free exciton (FE) and bound exciton (BE) recombinations, with the transverse optic (TO) replica, depends directly on the active dopant concentration and can be used to quantify independently donor and acceptor concentrations. Donors induce a BE TO recombination at 5.175 eV [10] while boron acceptors give a BE TO B recombination at 5.209 eV [11] and both peaks can be observed on the same spectrum [10]. Thus, in the case of a compensation of boron by donors, we expect to observe the two peaks but, if a full passivation of boron occurs, the boron-related BE TO B excitonic peak is expected to vanish as the excitons cannot anymore be bound to acceptors.…”

Influence of the substrate type on CVD grown homoepitaxial diamond layer quality by cross sectional TEM and CL analysis

“…The three substrates are a (110) IIIa CVD from E6 (sample A-PNV38), a (100) optical grade from E6 (sample B-PNV42), and a Ib HPHT from Sumitomo (sample C-PNV46). The growth consists of a 2 μm thick epilayer (see [11,12]) and the estimate growth velocity is 800 nm/h.…”

Diamond for Electronics: Materials, Processing and Devices

“…During the last two decades, CL has been demonstrated [93] to be an exceptional tool to evaluate the doping level [94] with an accuracy one order of magnitude better than secondary ion mass spectroscopy (SIMS). It also allows determining the type of point defects present in the crystal as H3 that are generated in the mid-gap [95]. Dislocations related to mid-gap levels (A-band) can be related to the presence of interfaces using monochromatic luminescence maps with a sub-micrometric resolution.…”