Y. Haddab

Evidence of interface trap creation by hot‐electrons in AlGaAs/GaAs high electron mobility transistors

We report on the hot‐electrons induced degradation in AlGaAs/GaAs high electron mobility transistors (HEMTs), consisting of a decrease in the drain current and an increase in the parasitic drain resistance. The amount of the degradation is proportional to the impact‐ionization rate which is related to the electron energy. Transconductance dispersion measurements and drain current deep level transient spectroscopy (DLTS) have been used to identify interface traps which are located at the AlGaAs/GaAs interface in the gate‐drain access region and are the causes of the observed degradation.

QUANTIZED CURRENT JUMPS IN SILICON PHOTOCONDUCTORS AT ROOM TEMPERATURE

We report on the observation of quantized jumps due to single-carrier trapping and detrapping at defect states in silicon photoconductors of 103 μm3 in volume. A specifically designed electrical test structure in a low-doped (2×1014 cm−3) silicon crystal was fabricated. It consists in four substrate resistances connected in a Wheatstone bridge. After the exposure to light, the bridge offset voltage recovers its equilibrium value with steps of 5–10 μV, corresponding to the emission or capture of a single carrier. Such structures also display random telegraph signals in the dark, with steps of similar amplitude. This behavior is observed with structures processed on Czochralski-grown substrates and not with those processed on float-zone substrates. Simple calculations based on quantized free carrier concentration variations corroborate the above measurements.

HOT CARRIER EFFECTS IN ALGAAS/INGAAS HIGH ELECTRON MOBILITY TRANSISTORS : FAILURE MECHANISMS INDUCED BY HOT CARRIER TESTING

A new failure mechanism of AlGaAs/InGaAs pseudomorphic high electron mobility transistors has been observed after hot carrier dc accelerated testing. Hot carrier effects have been characterized by means of gate current measurements and electroluminescence spectroscopy. After accelerated testing, a permanent degradation has been found, consisting of the decrease of drain current ID, and of the absolute value of the pinch-off voltage Vp, at low drain-source voltage VDS, resulting in the development of a remarkable “kink” in the output characteristics. Direct current, pulsed, and low-frequency ac measurements demonstrate that the failure mechanism consists of the creation of deep levels under the gate which act as electron traps at low gate-to-drain electric fields. Deep level transient spectroscopy and photoinjection measurements reveal the presence of two levels at 0.77 eV and 1.22 eV. The intensity of the 1.22 eV peak is correlated with the degradation observed in stressed devices.

A non-plate like Hall Sensor

Conventional Hall devices are plate-like, i.e., made in a thin semiconductor layer. We present here a Hall device made in a semi-infinite piece of semiconductor. Its active zone is limited by only one non-conductive surface. Although the base of the device is open, the part of the limited active zone filled by the current remains thin. The novel device exhibits a sensitivity of 0.33 V/mAT. We have shown that the characteristics of the non-plate like Hall device when its size is small asymptotically approach the characteristics of the conventional Hall plate. It opens the door to the realisation of 3D Hall device in the technology of the vertical Hall devices. In order to use the novel sensor as a stand-alone device, we improved it by an additional doping at the surface.

Observation of dopant–vacancy defects by low-frequency noise measurements in heavily doped n+/p+ silicon diodes

Abstract Low-frequency noise measurements have been performed at several temperatures for reverse biased silicon diodes heavily doped on both sides. The dopant impurities were boron and phosphorus. The analysis of the generation–recombination components of the noise spectrum showed two trap levels with an activation energy of 0.35 and 0.45 eV. These are typical of two defect complexes: the boron–vacancy pair and the phosphorus–vacancy pair, respectively. In spite of limited accuracy in the determination of activation energies, low-frequency noise measurements can therefore be used to detect such defect complexes, which can play an important part in understanding the diffusion in heavily doped silicon. Low-frequency noise spectroscopy appears to be the simplest technique available to measure such defects in silicon.

Hot carrier Hall devices in CMOS technology

The sensitivity of Hall devices for a given bias current is often limited by short circuiting effects due to the finite length of the structure. The reduction of the sensitivity is especially important in small devices where contacts occupy a large part of the active zone. In the present work, we present a novel method to enhance the current-related sensitivity. This is done by increasing the current till saturation which leads to the enhancement of the input impedance and thus to the limitation of short circuit. In sufficiently small devices the carrier velocity saturation is the main cause of the resistance increase. Other contributions to the sensitivity increase such as junction field effect and heating have been taken into account. With the help of computer simulations, we have separated the different contributions. The velocity saturation effect leads up to 40% increase in sensitivity near the breakdown voltage as compared to the low electric field Hall voltage. Although the sensitivity increases the overall performance has degraded when operating in the hot carrier regime.

Persistent photoconductivity as a tool for monitoring oxide cluster concentration in silicon wafers

Abstract Many semiconductor devices rely on the so-called “denuded zone” of the silicon wafers. It is therefore essential to have a simple means to monitor the purity of this zone. It will be shown that persistent photoconductivity (PPC) can be related to the oxygen concentration in the wafer, and thus can be used to evaluate the quality of the denuded zone. A test structure was designed and the PPC measurements performed. They clearly indicate that the intensity of the PPC effect is roughly proportional to the amount of oxygen clusters in the wafer.

Persistent photoconductivity in silicon wafers

Persistent photoconductivity effect in silicon wafers was observed using specifically designed test structures. Persistent changes in conductivity can reach 0.01% in wafers with a doping level of . The recovery time constant is in the range 10-30 min at room temperature. Oxygen-rich-Czochralski-grown wafers were compared with oxygen-poor float-zone-grown ones. The persistent photoconductivity is much higher in the Czochralski wafers. This indicates that this effect is most probably related to oxygen in silicon. To the best of our knowledge, such an effect has never been observed before in silicon crystals.

Influence of assembling procedure on IC parameters

In this paper we present a new test structure, consisting of an array of piezoresistors, for analyzing the influence of the packaging procedure on the stability of silicon IC device parameters. The test structure has been mounted onto the Printed Circuit Board (PCB) substrate. Bending of the substrate with the mounted chip has been performed. The results show that a special mounting technique, leaving the sensor area free standing, significantly improves the mechanical isolation of the sensor. Finite Element Method (FEM) simulations give us the same conclusions. Finally, stress induced effects on the test structure due to the wire bonding have been measured and a change of 0.8% in offset voltage in a Wheatstone bridge configuration has been reported.

Investigation of DX centers in modulation-doped field-effect transistor-type Al 0.3 Ga 0.7 As/GaAs heterostructures using a Fourier-transform deep level transient spectroscopy system

Al0.3Ga0.7As:Si/GaAs modulation-doped field-effect transistor-type heterostructures were grown using two different growth temperatures (500 and 620°C) and three doping modes (δ-doping, pulse-doping, and uniform-doping). Deep level transient spectroscopy (DLTS) measurements were performed on these structures using a new Fourier-analysis method. Up to four DLTS peaks, related to the different possible configurations of the nearest Al and Ga neighbors around each DX site, were observed. Both the growth temperature and the doping-mode are found to affect the DLTS spectra, in particular the number of observed peaks and their width. These results are interpreted in terms of the different mobilities of the Si doping atoms on the surface during growth.