Salvatore Vantaggio

Al+ Implanted 4H-SiC: Improved Electrical Activation and Ohmic Contacts

The p-type doping of high purity semi-insulating 4H-SiC by Al+ ion implantation and a conventional thermal annealing of 1950 °C/5 min has been studied for implanted Al concentration in the range of 1 x1019 - 8 x 1020 cm-3 (0.36 μm implanted thickness). Sheet resistance in the range of 1.6 x 104 to 8.9 x102 Ω, corresponding to a resistivity in the range of 4.7 x 10-1 to 2.7 x 10-2 Ωcm for increasing implanted Al concentration have been obtained. Hall carrier density and mobility data in the temperature range of 140–600 K feature the transition from a valence band to an intra-band conduction for increasing implanted Al concentration. The specific contact resistance of Ti/Al contacts on the 5 x1019 cm-3 Al implanted specimen features a thermionic field effect conduction with a specific contact resistance in the 10-6 Ωcm2 decade.

Modulation frequency dependence of the photoelectrical response of GaAs/InGaP superlattices

Photoelectrical measurements were taken on a nominally undoped-InGaP/GaAs superlattice, inserted between two p+ and n+ InGaP cladding layers. The sequence of InGaP/GaAs alternated layers forming the superlattice was grown lattice matched on n+-GaAs substrates through low pressure-metal organic vapor phase epitaxy, at growth conditions previously optimized for obtaining sharp interfaces and negligible ordering effects in the cation sublattice of the InGaP layers. A peculiar dependence of both the photocurrent and the photovoltaic signals on the modulation frequency of the exciting light beam was observed and then interpreted according to proper equivalent electrical circuits. The effects induced by an incomplete depletion of the nominally undoped superlattice region are analyzed in detail, and the analogies between photoelectrical investigation and admittance spectroscopy are pointed out.

1950°C Annealing of Al+ Implanted 4H-SiC: Sheet Resistance Dependence on the Annealing Time

This study shows that, after annealing at 1950°C, a 1×1020 cm-3 Al+ implanted 4H-SiC material shows a decreasing resistivity with increasing annealing time in the range 5-25 min. After this, the resistivity remains constant up to an annealing time of 40 min. The estimated minimum time to gain the thermal equilibrium in this implanted material at 1950°C is 12 min. Electrical characterization has been performed in the 20-680 K temperature range.

Anomalies in the Temperature Dependence of the Photoelectrical Response of GaAs/InGaP Superlattices

Photoelectrical measurements were taken on InGaP (p+)-GaAs/InGaP-InGaP (n+) multilayers structures, formed by a sequence of nominally undoped InGaP/GaAs quantum wells, interposed between two p+ and n+ InGaP cladding layers. The heterostructures were grown through Low Pressure Metal Organic Vapour Phase Epitaxy, with liquid precursors for the III–V elements and growth conditions optimized for obtaining sharp interfaces and negligible ordering effects in InGaP. The experimental temperature dependence of the photoelectrical signal intensity exhibited peculiarities and anomalies which could lead to erroneous analysis of the perpendicular transport mechanisms, so that they are here critically discussed in the light of a partial depletion of the nominally intrinsic superlattice region of the p–i–n structure.

Al+ Ion Implanted On-Axis Semi-Insulating 4H-SiC

P-type 4H-SiC layers have been obtained by different 400°C Al+ ion implantation processes of semi insulating 4H-SiC wafers and identical 1950°C/5 min post implantation annealing. Implanted Al+ concentration have been 4.7×1018, 9.3×1018, and 4.7×1019 cm-3, thickness of the implanted layer about 630 nm. Electrical characterizations have been performed in the temperature range 100 – 580 K. With decreasing temperature, the onset of a hole conduction through an impurity band has been seen for all the specimens.

Vertical transport through GaAs/InGaP multi-quantum-wells p-i-n diode with evidence of tunneling effects

Vertical transport in p-i-n diodes containing InGaP/GaAs multi-quantum-wells (MQW) is investigated using current-voltage measurements under forward bias at different temperatures. At low injection, the experimental data are analyzed through a two diode model, by taking into account the non-complete depletion of the MQW region caused by unintentional p-type doping. The diffusion current results to be dominant at high temperatures, whereas the current due to non-radiative recombination through defects in the space charge region becomes more and more relevant as the temperature is reduced. At temperatures above T = 150 K and at high forward voltages, when the current is limited by the series resistance, the thermionic emission of holes over the InGaP barriers controls the transport through the whole MQW region. At lower temperatures resonant tunneling of holes takes place and a simple picture of the hole quantum levels permits to interpret the main details of the I(V) curves at T = 41 K, by supporting the hy...