Precision admittance spectroscopy measurements were carried out over wide temperature and frequency ranges for a set of natural single crystal type IIb diamond samples. Peaks of conductance spectra vs. temperature and frequency were used to compute the Arrhenius plots, and activation energies were derived from these plots. The capacitance-voltage profiling was used to estimate the majority charge carrier concentration and its distribution into depth of the samples. Apparent activation energies between 315 and 325 meV and the capture cross section of about 10 -13 cm 2 were found for samples with uncompensated boron concentrations in the range of 1 to 5 x 10 16 cm -3 (0.06-0.3 ppm). The obtained boron concentrations are in good coincidence with FTIR results for the samples. Also, the reason the difference between the observed admittance activation energy and the previously reported ionization energy for the acceptor boron in diamond (0.37 eV) is proposed. Graphical abstract Highlights Admittance spectroscopy is a powerful and nondestructive technique, which allows one to obtain characteristics of electronic spectra for doped diamonds The combination of temperature and frequency admittance spectra give the convenient and tunable set of tools for the comprehensive analysis of impurity and defect levels, their activation energies and capture cross sections For the first time the activation energy and the capture cross section for boron deep center in natural diamond was obtained by admittance spectroscopy with high precision: for all natural "blue" diamonds (type IIb) the apparent activation energy is 315-325 meV, with the mean square error (MSE) for every sample no more than 1-2 meV. The reasons for the difference with the optical ionization energy is discussed
Light-emitting heterostructures with single and multiple GaAs/InGaAs quantum wells have been investigated by means of electrochemical capacitance-voltage (ECV) profiling. Capacitance-voltage characteristics were measured; concentration profiles of free charge carriers over the heterostructure depth as well as the intensity of quantum well filling by charge carriers were obtained. In heterostructures with a single quantum well (QW) we considered limitations of capacitance techniques for undoped QW profiling, which is situated near the metallurgic border of the p−n-junction. We made a detailed consideration of phenomena related to Debye smearing and we developed and analyzed the dependence of the space charge region width on the doping. Special attention was paid to investigation of the "blind" area. This was inspired by the practical problem from capacitance spectroscopy of semiconductors, when the researcher poses the task of obtaining a free charge carrier depth distribution profile as deep as possible in the space charge region, i.e. where the intensity of the electric field is maximum. Generally, the active QW of a LED heterostructure is placed deep in the space charge region, so reaching these regions is extremely important for practical problems. We present an evolution of capacitance-voltage characteristics during ECV profiling of nonuniformly doped p − n− heterostructures. For a heterostructure with multiple quantum wells we registered a response from 6 QWs.
We present experimental and theoretical investigations of pHEMT heterostructures with AlGaAs/InGaAs/GaAs quantum wells (QWs) and/or a delta-doped layer, which can be used as active regions in transistors operating in the 4-18 GHz frequency range. Using the electrochemical capacitance-voltage setup ECV Pro we, for the first time, experimentally observed a concentration peak from the near-surface delta layer of the pHEMT structure together with a peak of QW enrichment. The capacitance of the electrolyte-semiconductor contact was measured by Agilent LCR-meter, which was connected to the electrochemical cell of ECV Pro through a specially designed relay module. Using numerical simulation of the electronic characteristics of nanoheterostructures by self-consistent solution of Schrödinger and Poisson equations we determined electrostatic potential profiles for band edges, band offsets, quantum-confinement levels, and concentration profiles of charge carriers for the samples under investigation. The impact of delta-layer position on the confined energy levels and carrier concentration in the QW was experimentally and theoretically analyzed in detail. We determined the optimal distance between the QW and delta layer, which provides the most efficient process of supply of charge carriers to the QW. The conducted work is directed at improvement of SHF devices, allowing one to increase the gain coefficient and transconductance of transistors.
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