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Boron incorporation issues in diamond when TMB is used as extreme doping levels

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HAL-CEA
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  • [Spi.Gproc] Engineering Sciences [Physics]/Chemical And Process Engineering
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Abstract

Boron doped diamond (BDD) is a very promising material for high frequency and high power applications like Field Emission Transistors and Schottky diodes. Such electrical devices are usually composed of stacked highly BDD layers ([B]> 5x 10(20) at.cm(-3)) on doped at low levels ones ([B] < 10(17) at.cm(-3)). In particular, when delta doping structures are sought, their development implies the accurate control of the highly BDD layer thickness at the nanometric scale, and, the achievement of high crystalline quality for low BDD layers with, well defined doping gradients and low roughness at the interfaces. Since several decades, various gaseous precursors, most frequently diborane (B2H6) and TriMethylBoron-TMB (B(CH3)(3)), have been used to grow BDD layers. TMB is generally seen as a good alternative to diborane as it is less toxic and easier to handle while it offers expected similar doping properties. In this study, we determine several strategies to grow, using in a metallic wall MPCVD reactor with TriMethylBoron (TMB, B(CH3)(3)) as dopant, high crystalline quality very poorly and highly doped (100) diamond layers. We investigated a wide boron incorporation ([BI) typically between 10(16) at "cm-3 up to 5 x 10(21) at.cm(-3). We will especially insist on two growth strategies to produce monocrystalline diamond doped at low levels, consisting either to use very low (B/C)g ratio during growth, or to feed oxygen during growth at a constant (B/C)g ratio. Comparison of these two strategies will be assessed from low temperature Cathodoluminescence (CL), Secondary Ion Mass Spectroscopy (SIMS), C(V) and Hall effect measurements on several layers. The effects of oxygen on boron atoms, when TMB is used as doping gas will also be studied in detail and commented. In a second part, we will especially investigate the synthesis of highly BDD diamond layers ([B]> 5x 10(20) at.cm(-3)). SIMS analysis enables to identify the existing links between growth conditions ([CH4]/[H-2] and (B/C)(gas) ratios, pressure, temperature) and the boron incorporation into the diamond matrix. We will finally show that, under optimized growth regimes, the metallic-semiconductor transition above 10(21) at.cm(-3) of boron can be routinely achieved.

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