Nanometric diamond delta doping with boron

Abstract

Introduction The semiconductor single-crystal CVD diamond (ob-tained from the gas phase during homoepitaxial deposi-tion) is a wide band gap semiconductor with a gap width of 5.5 eV. CVD diamond has unique characteristics-high mobility of charge carriers, high carrier saturation speed, high electric breakdown field, the greatest thermal conductivity, high radiation and chemical resistance. On a combination of properties the CVD diamond is superior to other wide band gap semiconductors and is considered a promising material for the creation of a new generation of high-power and high-frequency electronic devices. The main difficulty in realization of the potential of CVD diamond as an electronic material is the problem of creating charge carriers inside it. Compared with conventional semiconductors, dopants in diamond have deeper energy levels that significantly impede the activation of the do-pant (the degree of ionization of the dopant at room temperature is less than 1%). Thus, in order to create an acceptable level of conductivity, it is necessary to increase the level of doping, but in case of boron doping this leads to a decrease of carriers (holes) mobility in diamond. To solve the problem of boron doping of CVD diamond, an approach based on delta-doping technology is known. A thin layer of diamond heavily doped with boron (hav-ing a thickness of 1-2 nm and concentration of boron atoms higher than 5×10 20 cm-3) is formed inside an un-doped defect-free diamond of high quality. To achieve high electronic properties (obtaining high hole mobility and conductivity of the layer), it is necessary to realize sharp boundaries between the doped and undoped materials. Recently, this problem has been successfully solved [1, 2]. This report provides an overview of the results of studies on the growth of electronic-quality epitaxial layers of diamond, the production of heavily boron-doped layers and the study of their characteristics. Experiments The novel microwave plasma assisted CVD reactor for growth of nanometric boron delta-doped layers with ultra-sharp interfaces between doped/undoped materials was built in IAPRAS [1]. Fig. 1 shows a schematic of the reactor. The main features of the reactor are: 1) rapid gas switching; 2) laminar gas flow; 3) axial symmetric resonant mode-symmetric discharge; 4) slow growth of diamond 40-100 nm/h. We achieve rapid gas switching from one input gas to another by a home-made electronic switch. The residence time of the reactor is approximately 5 s. In developed reactor the diamond deposition regimes in which one obtains thin doped delta layers with thickness of 1-2 nm with concentrations of boron about 5·10 20 cm-3 were found. Typical parameters of the delta layer under these conditions are given in Fig. 2 for the SS6-1 sample, in which the boron concentration is 4.8·10 20 cm-3 and thickness is 1 nm. Measurement of the boron concentration in the grown samples was carried out by the secondary ion mass spectroscopy (SIMS) method using a time of flight SIMS setup (IONTOF TOF.SIMS-5). T...

Progress Toward Diamond Power Field‐Effect Transistors

“…Only recently has a diamond growth system been specifically designed for delta doping using very smooth starting diamond substrates. It has shown promising initial results, detailed in works by Butler and Lobaev et al For the first time to these authors’ knowledge resistances <10 kΩ sq −1 (1.1 to 7 kΩ sq −1 ) with mobilities from 16 to 120 cm 2 V −1 s −1 (approaching the predicted mobilities of 150 to 200 cm 2 V −1 s −1 ) have been consistently obtained. Their experimental setup is similar to others.…”

“…For comparison, if the boron was uniformly distributed, <1% of the boron atoms would contribute holes, making the material too resistive through both low carrier density and degraded mobility. There are numerous reports on delta‐doped diamond, but the device quality of these layers has been disappointing until recently …”

“…The only known technique that could generate such a diamond structure is epitaxial growth with exquisite control over the starting diamond surface roughness, growth rate, impurities, and boron dopant. Several attempts to create such a structure have been reported, but electrical measurements did not show the expected low resistance and high mobilities . Kohn suggested that the poor result is due to nonuniform boron doping in the delta layer, resulting in boron clusters, which he observed in cross sectional high‐resolution transmission electron microscopy, HR‐TEM.…”

Омические Контакты К Эпитаксиальным Структурам CVD-алмаза С Дельта-Слоями Бора

“…В последнее время большой интерес вызывает развитие технологии изготовления монокристаллических пленок алмаза с δ-слоями бора [1][2][3][4][5][6][7][8]. Такие структуры рассматриваются как перспективный полупроводниковый материал с новыми транспортными свойствами.…”

CVD diamond with boron-doped delta-layers deposited by microwave plasma

“…To achieve high electronic properties (obtaining high hole mobility and conductivity of the layer), it is necessary to realize sharp boundaries between the doped and undoped materials. Recently, this problem has been successfully solved [1,2]. This report provides an overview of the results of studies on the growth of electronic-quality epitaxial layers of diamond, the production of heavily boron-doped layers and the study of their characteristics.…”