L. Bailón

Admittance spectroscopy in junctions

Abstract The techniques based on the measurement of admittance used for characterization of deep levels are reviewed in this paper. Thermal admittance spectroscopy is a technique which allows the measurement of thermal emission rates and thermal activation energies of deep levels in junctions. Optical admittance spectroscopy allows the measurement of optical capture cross sections and optical threshold energies of deep levels in junctions. Thermal admittance spectroscopy can also be applied to III–V alloy junctions in order to characterize the thermal properties of DX centres, which typically appear in these materials. Finally, we show that optical admittance spectroscopy applied to junctions containing DX centres should yield the optical properties of these centres.

Influence of single and double deposition temperatures on the interface quality of atomic layer deposited Al2O3 dielectric thin films on silicon

An electrical characterization of Al2O3 based metal-insulator-semiconductor structures has been carried out by using capacitance-voltage, deep level transient spectroscopy, and conductance-transient (G-t) techniques. Dielectric films were atomic layer deposited (ALD) at temperatures ranging from 300 to 800 °C directly on silicon substrates and on an Al2O3 buffer layer that was grown in the same process by using 15 ALD cycles at 300 °C. As for single growth temperatures, 300 °C leads to the lowest density of states distributed away from the interface to the insulator [disorder-induced gap states (DIGS)], but to the highest interfacial state density (Dit). However, by using 300∕500°C double growth temperatures it is possible to maintain low DIGS values and to improve the interface quality in terms of Dit. The very first ALD cycles define the dielectric properties very near to the dielectric-semiconductor interface, and growing an upper layer at higher ALD temperature produces some annealing of interfacial s...

Improved binary collision approximation ion implant simulators

An efficient binary collision approximation (BCA) ion implant code with good prediction capabilities for semiconductor materials (Si, GaAs, SiC) with only one fitting parameter for low implantation doses is presented. It includes specific interatomic potentials and recent improvements in physical models for inelastic stopping. A periodic ab initio full bond electron density for the target is used. Damage accumulation is supported using a modified Kinchin–Pease model [G. H. Kinchin and R. S. Pease, Rep. Prog. Phys. 18, 1 (1955)]. Also, some of the BCA integration algorithms and target selection procedure have been refined. An algorithm commonly used for statistical noise reduction has been modified to also improve the noise reduction in the lateral and shallow zones. The agreement with experiments is good, even under channeling conditions and for different target materials. A comparison with experimental secondary ion mass spectroscopy results for several projectiles and targets is presented.

Electrical Properties of Atomic-Layer-Deposited Thin Gadolinium Oxide High-k Gate Dielectrics

Amorphous or cubic Gd2O3 thin films were grown from tris ( 2,3-dimethyl-2-butoxy)gadolinium( III) , Gd [OC(CH3)(2)CH(CH3)(2))(3)], and H2O precursors at 350 degrees C. As-deposited Gd2O3 films grown on etched (H-terminated) Si(100) exhibited better leakage current-voltage characteristics as well as lower flatband voltage shift than films grown on SiO2/ Si substrates. Interface trap densities were lower in Al/Gd2O3/ hydrofluoric acid (HF)-etched Si samples annealed at rather high temperatures.

Optical admittance spectroscopy: A new method for deep level characterization

A new method for the optical cross‐section measurement of deep levels in junctions is presented. It is based on the measurement of the capacitance and conductance of the junction under illumination, as a function of the photon energy hν and the frequency of the measuring signal. This technique has been applied to the measurement of the optical capture cross section σon of the Au acceptor level corresponding to the emission of electrons to the conduction band.

Influence of interlayer trapping and detrapping mechanisms on the electrical characterization of hafnium oxide/silicon nitride stacks on silicon

Al/HfO2/SiNx:H/n-Si metal-insulator-semiconductor capacitors have been studied by electrical characterization. Films of silicon nitride were directly grown on n-type silicon substrates by electron cyclotron resonance assisted chemical vapor deposition. Silicon nitride thickness was varied from 3 to 6.6 nm. Afterwards, 12 nm thick hafnium oxide films were deposited by the high-pressure sputtering approach. Interface quality was determined by using current-voltage, capacitance-voltage, deep-level transient spectroscopy (DLTS), conductance transients, and flatband voltage transient techniques. Leakage currents followed the Poole–Frenkel emission model in all cases. According to the simultaneous measurement of the high and low frequency capacitance voltage curves, the interface trap density obtained for all the samples is in the 1011 cm−2 eV−1 range. However, a significant increase in this density of about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride interfacial layers. In thi...

Electrical properties of thin zirconium and hafnium oxide high-k gate dielectrics grown by atomic layer deposition from cyclopentadienyl and ozone precursors

ZrO2 and reference HfO2 films grown by atomic layer deposition from metal cyclopentadienyls and ozone as precursors to thicknesses ranging from 3.6to13.1nm on etched silicon showed electrical characteristics adequate to high-k dielectrics. The best results in terms of low interface state densities were obtained when (CpMe)2ZrMe2 precursor was used, with Cp denoting the cyclopentadienyl group (C5H5), and Me the methyl group (CH3). The ZrO2 films grown from (CpMe)2Zr(OMe)Me possessed nearly an order of magnitude higher trap state densities. Similar dependence on the precursor chemistry was observed upon recording the flatband voltage time transients. The flatband voltage transients, originating from phonon-assisted tunneling between localized states at oxide silicon interface, were the lowest in HfO2 films grown from (CpMe)2Hf(OMe)Me. The leakage current densities were also lower in the HfO2 films, compared to ZrO2. On the other hand, interfacial trap state densities in HfO2 based capacitors remained higher...

Electrical properties of high-pressure reactive sputtered thin hafnium oxide high-k gate dielectrics

Thin films of hafnium oxide have been deposited by the high-pressure reactive sputtering (HPRS) system. In this growth system the deposition pressure is around 1 mbar, three orders of magnitude higher than in the conventional ones, assuring that both reflected and sputtered particles reach the substrate with a low energy. The amorphous or polycrystalline structure is modified by adjusting the ratio of oxygen to argon of the sputtering gas. The electrical characteristics of both polycrystalline and amorphous films are compared. In all cases, the leakage current can be fitted to Poole–Frenkel emission. Amorphous films show the best characteristics in terms of capacitance–voltage behaviour, leakage current and interfacial state density, with conductance and flat-band voltage transients almost negligible.

The Poole-Frenkel effect in 6H-SiC diode characteristics

The large bandgap of SiC makes the recombination mechanism the main process in determining the forward current in a large range of temperature. We have added the Poole-Frenkel effect to the conventional Shockley-Read-Hall (SRH) term of the numerical device simulator MEDICI. This paper shows the influence of this effect on SiC. >

Experimental verification of intermediate band formation on titanium-implanted silicon

Intermediate band formation on silicon layers for solar cell applications was achieved by titanium implantation and laser annealing. A two-layer heterogeneous system, formed by the implanted layer and by the un-implanted substrate, was formed. In this work, we present for the first time electrical characterization results which show that recombination is suppressed when the Ti concentration is high enough to overcome the Mott limit, in agreement with the intermediate band theory. Clear differences have been observed between samples implanted with doses under or over the Mott limit. Samples implanted under the Mott limit have capacitance values much lower than the un-implanted ones as corresponds to a highly doped semiconductor Schottky junction. However, when the Mott limit is surpassed, the samples have much higher capacitance, revealing that the intermediate band is formed. The capacitance increasing is due to the big amount of charge trapped at the intermediate band, even at low temperatures. Ti deep levels have been measured by admittance spectroscopy. These deep levels are located at energies which vary from 0.20 to 0.28 eV below the conduction band for implantation doses in the range 10(13)-10(14) at./cm(2). For doses over the Mott limit, the implanted atoms become nonrecombinant. Capacitance voltage transient technique measurements prove that the fabricated devices consist of two-layers, in which the implanted layer and the substrate behave as an n(+)/n junction.