Reverse Biased Silicon Research Articles

Near-infrared and mid-infrared light emission of boron-doped crystalline silicon.

The bottleneck in achieving fully integrated silicon photonics lies in silicon-based light-emitting devices that are compatible with standard CMOS technology. Dislocation loops created by implanting boron into silicon and annealing represent an enticing strategy to transform highly inefficient silicon into a luminescent material. However, the emission at telecommunication wavelength suffers from the strong thermal quenching effect, resulting in low efficiency at room temperature. Here, we applied a new deep cooling process to address this issue. Interestingly, we find that electrons and holes recombine through defects emitting two photons, one in near infrared (NIR, 1.3∼1.6 µm) and the other in mid-infrared band (MIR, around 3.5 µm). The photoluminescence intensity at NIR increases three fold when the temperature increases from 77 K to 300 K. Furthermore, the NIR light emission of reverse biased silicon diodes was significantly enhanced compared to forward bias, emitting the maximum output power of 42 nW at 60 mA. The results offer new opportunities for the development of infrared light sources in integrated circuits.

A Robust Quantum Random Number Generator Based on an Integrated Emitter-Photodetector Structure

We present a new compact photonic quantum random number generator based on an emitter (source of entropy) and a single-photon detector integrated in the same silicon chip. Not only they are integrated one close to the other, but also they are fabricated with the same fabrication process. The emitter is a small silicon photomultiplier, composed of passively-quenched single photon avalanche diodes (SPADs), having the same layout of the single SPAD used as the detector. The emitter is a reverse-biased silicon p-n junction, generating photons mainly due to impact ionization during the avalanche breakdown process. The detector is shielded from ambient light by a top metal layer: only photons from the emitter are detected, making this integrated approach more robust. The random bits are extracted with a robust methodology based on the measurement of photon arrival times, using discrete time bins, in a time frame cyclically repeated in time. No postprocessing is required for the raw data to pass the statistical tests.

Observation of electron excitation into silicon conduction band by slow-ion surface neutralization

Bare reverse biased silicon photodiodes were exposed to 3 eV He+, Ne+, Ar+, N2+, N+ and H2O+ ions. In all cases an increase of the reverse current through the diode was observed. This effect and its dependence on the ionization energy of the incident ions and on other factors are qualitatively explained in the framework of Auger-type surface neutralization theory. Amplification of the ion-induced charge was observed with an avalanche photodiode under high applied bias. The observed effect can be considered as ion-induced internal potential electron emission into the conduction band of silicon. To the best of our knowledge, no experimental evidence of such effect was previously reported. Possible applications are discussed.

Operando x-ray photoelectron emission microscopy for studying forward and reverse biased silicon p-n junctions.

Significant progress in the understanding of surfaces and interfaces of materials for new technologies requires operando studies, i.e., measurement of chemical, electronic, and magnetic properties under external stimulus (such as mechanical strain, optical illumination, or electric fields) applied in situ in order to approach real operating conditions. Electron microscopy attracts much interest, thanks to its ability to determine semiconductor doping at various scales in devices. Spectroscopic photoelectron emission microscopy (PEEM) is particularly powerful since it combines high spatial and energy resolution, allowing a comprehensive analysis of local work function, chemistry, and electronic structure using secondary, core level, and valence band electrons, respectively. Here we present the first operando spectroscopic PEEM study of a planar Si p-n junction under forward and reverse bias. The method can be used to characterize a vast range of materials at near device scales such as resistive oxides, conducting bridge memories and domain wall arrays in ferroelectrics photovoltaic devices.

Measurement and modeling of reverse biased electroluminescence in multi-crystalline silicon solar cells

Calibrated microscopic measurements of electroluminescent emission spectra of reverse biased multi-crystalline silicon solar cells in a wide range of photon energies E (0.8 eV ≤ E ≤ 4 eV) are reported. The observed spectra originating directly from point-like sources exhibit a broad maximum around 0.8 eV followed by a high photon energy tail. A model for intraband emission accurately fits microscopically measured spectra obtained from single point sources. Furthermore, we do not find significant features from interband recombination. From the fits to the intraband transition model, we extract an effective charge carrier temperature of around 4000 K for all investigated spots. The analysis also yields the different depths of the sources, which are shown to be consistent with the dimension of the space charge region. From the areas around the point sources, we observe indirect emission of internally reflected light. Due to the multiple paths through the wafer, this indirect emission exhibits a maximum at a photon energy slightly lower than the band gap energy Eg. We demonstrate that global, non-microscopic measurements are strongly influenced by this indirect radiation and therefore prone to misinterpretation.

Reverse I-V Behaviour of SiC Schottky Diodes Under Various Temperatures and Magnetic Fields

In this paper we present a study of reverse biased Silicon Carbide Schottky diodes under various magnetic fields and temperatures. The project involved four samples of the same nature but different packages of their pairs. Silicon carbide is a material of recent use in the field of electronics. It is used for the manufacture of electronic components operating in high power, high voltage, high temperature and high frequency because of its physical and chemical properties conducive to its operation in the areas mentioned. Among the components made from silicon carbide, bipolar and MOS transistors and Schottky diodes. These components are currently operating at voltages of about 1200V, and can handle currents of 20A, which allow them to be used in an environment of very high power and high temperature. To carry out the measures, Oxford Teslatron system was used for the characterization of low reverse voltage samples as a magnetic field and for temperatures below room temperature. In high reverse voltages and depending temperature study was performed without magnetic field. Through the I (V) and C reverse (V), we studied the effect of temperature and magnetic field on the saturation current I S, to determine the barrier height of the junction and the nature of Anode transport. The reverse IV characteristics measurements were recorded at temperatures ranging from 100 ° to 300 ° k and k without magnetic field and then 300k to 473 k no field. The effect of the magnetic field was demonstrated by plotting the relative changes in current and reverse saturation current. We also infers that there is not a phenomenon of saturation current I S due to deep traps in the structure and that the phenomenon of transport is by thermionic emission assisted by field effect.

Natural fluctuations in tunneling-current distribution over the area of a reverse-biased silicon p-n junction

The Monte Carlo method is used for calculating the distributions of the electric field, potential, and interband-tunneling probability over the area of a reverse-biased p-n junction, taking into account the discreteness of the charge distribution of ionized donors and acceptors. The calculations are carried out in a three-dimensional approximation on the basis of the principle of superposition of the electric fields of “ionized-donor-ionized-acceptor” ion pairs. It is shown that, in the region of clusters of three or more ion pairs with the characteristic distance of about half of the de-Broglie wavelength between them, an increase in the tunneling probability related to a local increase in the electric-field strength is observed.

Local investigation of thermal dependence of light emission from reverse-biased monocrystalline silicon solar cells

The quality and lifetime of solar cells critically depend on minimization of both bulk and surface imperfections. When a solar cell is reverse-biased with low voltage, weak emission from imperfections (pre-breakdown sites) appears. We report on the local measurement of such breakdown using a scanning near-field optical microscope. Due to the very weak signals, we use a cooled photomultiplier in the photon counting regime to achieve high sensitivity light detection. This technique allows non-destructive detection, localization and high spatial resolution of light-emitting centers originating from different imperfections in the cell. We have found that the emission from these pre-breakdown sites exhibits unique thermal characteristics. As a consequence, the thermal characteristics can distinguish among several kinds of imperfections in monocrystalline silicon solar cells.

Broadband linearized silicon modulator

A scheme to achieve a wideband linearized silicon Mach-Zehnder (MZ) modulator is proposed. The modulator consists of a single MZ interferometer with identical reverse-biased silicon diode phase shifters in both arms, driven in a push-pull configuration. It is shown that the 3rd order nonlinearity of the modulator can be eliminated by canceling the nonlinearities from the silicon phase shifters and the MZ transfer function against each other. The 2nd order nonlinearity is simultaneously eliminated by differential detection or operation away from the quadrature point. As a result, the linearity of the proposed silicon modulator greatly exceeds the linearity of a conventional MZ modulator with ideal, linear (e.g. LiNbO3) phase shifters. The simplicity and large optical and RF bandwidth of the proposed modulator make it attractive for analog photonic applications.

On the nature of electroluminescence at 1.5 μm in the breakdown mode of reverse-biased Er-doped silicon p-n-junction structures grown by sublimation molecular beam epitaxy

Electroluminescence features in the wavelength range of 0.9–1.65 μm were experimentally studied in the breakdown mode of reverse biased Si/Si:Er/Si p-n-junction structures grown by sublimation molecular-beam epitaxy. Based on the results of this study, a new physical model is proposed, in which radiative transitions in the near-infrared region are excited by recombination of electrons arriving at corresponding energy levels in the Si:Er layer due to their tunneling from the valence band of the p+-layer in the electric field of the reverse biased p-n-junction. The model proposed is in qualitative agreement with main available experimental results.

Luminescence emission from forward- and reverse-biased multicrystalline silicon solar cells

We study the emission of light from industrial multicrystalline silicon solar cells under forward and reverse biases. Camera-based luminescence imaging techniques and dark lock-in thermography are used to gain information about the spatial distribution and the energy dissipation at pre-breakdown sites frequently found in multicrystalline silicon solar cells. The pre-breakdown occurs at specific sites and is associated with an increase in temperature and the emission of visible light under reverse bias. Moreover, additional light emission is found in some regions in the subband-gap range between 1400 and 1700 nm under forward bias. Investigations of multicrystalline silicon solar cells with different interstitial oxygen concentrations and with an electron microscopic analysis suggest that the local light emission in these areas is directly related to clusters of oxygen.

X-ray tests of a Pixel Array Detector for coherent x-ray imaging at the Linac Coherent Light Source

Test results are presented of a pixel array detector (PAD)developed for x-ray imaging at the Stanford Linear Coherent LightSource (LCLS). The basic module of the PAD consists of twobump-bonded chips: a reverse-biased silicon diode chip of 185 × 194 pixels, each of which is coupled by bump-bonds to acharge integrating CMOS ASIC with digitization in each pixel. TheLCLS experiment requires a high signal-to-noise ratio for detectionof single 8 keV x-rays, a pixel full-well exceeding1,000 8 keV x-rays, a frame-rate of 120 Hz, and the ability to handle the arrival of thousands ofx-rays per pixel in tens of femtoseconds. Measurements haveverified a pixel full-well value of 2,700 8 keVx-rays. Single 8 keV photon detection has been shownwith a signal-to-noise ratio of >6. Line-spread responsemeasurements confirmed charge spreading to be limited to nearestneighbor pixels. Modules still functioned after dosages up to 75 Mrad(Si) at the detector face. Work is proceeding toincorporate an array of modules into a large-area detector.

A simple approach to the simulation of impact excitation of erbium in silicon light-emitting diodes

A simple numerical model for the impact excitation of erbium ions by hot carriers in reverse-biased erbium-doped silicon light-emitting diodes (LEDs) is proposed. The model involves the difference in Er3+ excitation efficiencies by hot electrons and holes. Comparative analysis of the Er3+ excitation efficiencies in LEDs with different electric field profiles in the space charge region of the diodes is performed. The estimations show that Er3+ electroluminescence intensity and excitation efficiency may be essentially increased (up to an order of magnitude compared to the widely studied p+/n-Si:Er LEDs) in the tunnelling transit-time p+/n+/n−-Si:Er diodes.

Behavior of an optical sensor based on non-ideal silicon capacitors: From amplification to generation

The behavior of reverse-biased silicon optical sensors based on non-ideal metal–leaky insulator–silicon (MLIS) capacitors was studied. A highly conductive tin-doped indium oxide film was used as a transparent metallic gate deposited on a leaky insulator containing many through pores. The tin-doped indium oxide, by penetrating in these pores, forms microscopic Schottky diodes on the n-silicon surface. The accumulation of the photo-generated holes under pores-free regions of the insulator surrounding these small-size Schottky diodes gives rise to the experimentally obtained photocurrent gain and self-sustained current oscillations, with a period that depends on the irradiation intensity. The modulation of the Schottky barrier height along the perimeter of the diodes by the holes accumulated under the insulator surrounding these diodes is suggested to explain the behavior of these MLIS structures. The validity of this model was verified by observing a similar behavior in optical sensors with a thermally grown silicon dioxide layer on the silicon surface. In such a case, microscopic Schottky diodes were formed by the penetration of the gate material in small-size “windows” specially etched in the silicon dioxide.

Displacement damage-induced catastrophic second breakdown in silicon carbide Schottky power diodes

A novel catastrophic breakdown mode in reverse biased silicon carbide diodes has been seen for particles that are too low in LET to induce SEB, however SEB-like events were seen from particles of higher LET. The low LET breakdown mechanism correlates with second breakdown in diodes due to increased leakage and assisted charge injection from incident particles. Percolation theory was used to predict some basic responses of the devices.

Double electron drift device as a magnetic field sensor

A new magnetic field sensor based on electron transport in the depletion region of reverse-biased silicon pin diodes is presented. Its field sensitivity is derived from transport equations with magnetic fields. The new sensor consists of a pin diode across the silicon wafer, an injection line within the anode, and opposite to this line a gap, which splits the cathode into two halves. The fabrication of the pin diodes is compatible with CMOS technology. The fabrication required layer processing on both wafer sides, transfer of alignment markers from one side to the other. Magnetic measurements revealed the following main results: the magnetic field sensitivity was 1.6 T−1, i.e. 23 times larger than that of Hall probes. All measured field sensitivities were in accordance with theoretical predictions. At high injection currents a reduction of the field sensitivity is observed which is caused by beam broadening due to space charge effects. Due to the alignment accuracy of less than ±1 μm magnetic offsets of up to 0.05 T were observed.

Off-axis electron holography of electrostatic potentials in unbiased and reverse biased focused ion beam milled semiconductor devices.

Off-axis electron holography in the transmission electron microscope (TEM) is used to measure two-dimensional electrostatic potentials in both unbiased and reverse biased silicon specimens that each contain a single p-n junction. All the specimens are prepared for examination in the TEM using focused ion beam (FIB) milling. The in situ electrical biasing experiments make use of a novel specimen geometry, which is based on a combination of cleaving and FIB milling. The design and construction of an electrical biasing holder are described, and the effects of TEM specimen preparation on the electrostatic potential in the specimen, as well as on fringing fields beyond the specimen surface, are assessed.

Double electron drift device as a magnetic field sensor

A new magnetic field sensor based on electron transport in the depletion region of reverse-biased silicon pin diodes is presented. Its field sensitivity is derived from transport equations with magnetic fields. The new sensor consists of a pin diode across the silicon wafer, an injection line within the anode, and opposite to this line a gap, which splits the cathode into two halves. The fabrication of the pin diodes is compatible with CMOS technology. The fabrication required layer processing on both wafer sides, transfer of alignment markers from one side to the other. Magnetic measurements revealed the following main results: the magnetic field sensitivity was 1.6 T −1, i.e. 23 times larger than that of Hall probes. All measured field sensitivities were in accordance with theoretical predictions. At high injection currents a reduction of the field sensitivity is observed which is caused by beam broadening due to space charge effects. Due to the alignment accuracy of less than ±1 μm magnetic offsets of up to 0.05 T were observed.

Transient effects on high voltage diode stack under reverse bias

This article describes and analyses the fast transient processes that can occur during a local non-destructive breakdown in a circuit consisting of a serial connection of reverse biased high-voltage silicon diodes. Measurements of the reverse current–voltage characteristics of the individual diodes showed that a breakdown had occurred. However, this phenomenon is very difficult to study when there are many diodes connected in series in a stack. A physical model was therefore created to show the individual local breakdown in this case. The validity of the model was verified by means of circuit simulation of the process under investigation. The statistical significance of the process was considered with respect to the reliability and lifetime of a high-voltage diode stack.

Reverse biased porous silicon light-emitting diodes for optical intra-chip interconnects

We have reported recent progress in development of the integrated optoelectronic unit on a Si chip. The developed optoelectronic unit includes a porous Si light-emitting diode (LED) connected with a photodetector by an alumina waveguide. Main attention has been devoted to the enhancement of LED parameters. Quantum efficiency as high as 0.4% has been reached. The delay time of 1.2 ns and the rise time of 1.5 ns have been measured for the diodes. Further improvements are also discussed.