Investigation of the thermal stability of picosecond gallium arsenide dynistor switches

The operation of GaAs n⁺-p-i-n ⁰-p ⁺ dynistor structures has been demonstrated experimentally under conditions of reversible avalanche breakdown at temperatures up to 200 °C with switching times remaining under 140 ps. A numerical simulation refined the influence of various parameters of the semiconductor on the temperature dependence of the switching characteristics. Pis’ma Zh. Tekh. Fiz. 24, 73–78 (August 12, 1998)     

Experimental Observation of Delayed Impact-Ionization Avalanche Breakdown in Semiconductor Structures without p–n Junctions

We have experimentally studied the dynamics of impact-ionization switching in semiconductor structures without p–n junctions when subnanosecond high-voltage pulses are applied. Silicon n⁺–n–n⁺ type structures and volume ZnSe samples with planar ohmic contacts exhibit reversible avalanche switching to the conducting state within about 200 ps, which resembles the well-known phenomenon of delayed avalanche breakdown in reverse-biased p⁺–n–n⁺ diode structures. Experimental data are compared to the results of numerical simulations.

     

Single photon counting at telecom wavelength and quantum key distribution

Abstract

A brief overview is given of single photon detector performance requirements for quantum cryptography applications. The analysis is made with respect to restrictions necessary to secure the quantum key distribution channel. InGaAs/InP avalanche photodiode performance is analysed for single photon counting at 1550 nm. Quantum efficiency, dark current and afterpulsing probability (for times up to 100μs after an initial avalanche) are studied in a wider temperature range than previously reported (0deg; C to –80deg;C). We show that photon counting is a bottle-neck in current quantum key distribution systems and provides the source for future performance improvement.     

Evolution and prospects for single-photon avalanche diodes and quenching circuits

Abstract

The evolution of solid-state avalanche detectors of single optical photons is outlined and the issues for further progress are discussed. Physical phenomena that underlay the operation of the single-photon avalanche diodes (SPAD) and determine the performance are considered and their role is assessed (detection efficiency; dark-counting rate; afterpulsing; photon timing resolution; etc.). The main technological issues that hamper the development of detectors with wide sensitive area and of array detectors with high filling factor are illustrated. Silicon SPADs are the main focus of attention; infrared-sensitive SPADs in germanium and in compound semiconductors are also dealt with. The role of the active-quenching circuits (AQC) is assessed and the evolution is outlined up to integrated AQCs, which offer the prospect of monolithic integration of complete photon counter instruments.     

Charge Carrier Transport and Deep Levels Recharge in Avalanche S-Diodes Based on GaAs

Carrier transport and deep-level recharging in semiconductor avalanche S-diode structures have been investigated. Gallium-arsenide n⁺–π–ν–n structures with the diffusion distribution of deep iron acceptors have been studied. It has been found by solving the continuity and Poisson equations with the use of a commercial software that the electron injection affects the avalanche breakdown voltage and the spacecharge region broadens due to capture of avalanche holes on negative iron ions in the π-region. It is demonstrated by comparing the results of numerical calculation with the experimental data that the S-shaped I–V characteristic of the diffusion avalanche S-diodes cannot be explained within the previously proposed mechanism of capture of avalanche holes on the deep iron levels.     

Subnanosecond avalanche switching in high-voltage silicon diodes with abrupt and graded p-n junctions

The phenomenon of delayed avalanche breakdown in high-voltage silicon diodes has been studied for the first time using an experimental setup with specially designed resistive coupler as a part of a high-quality matched measuring tract. Three types of diode structures with identical geometric parameters and close stationary breakdown voltages within 1.1–1.3 kV have been studied, including p ⁺-n-n ⁺ structures with abrupt p-n junctions and two different p ⁺-p-n-n ⁺ structures with graded p-n junctions. Upon switching of all structures, a voltage step with an amplitude above 1 kV and a rise time of ～100 ps at a breakdown voltage of about 2 kV is formed in the load. However, switching to a state with low (～150 V) residual voltage has been observed only in the structures with an abrupt p-n junction, while the voltage in structures with graded junctions only decreased to a level of ～1 kV, which is close to the stationary breakdown voltage.     

Detector efficiency limits on quantum improvement

Abstract

Although the National Institute of Standards and Technology has measured the intrinsic quantum efficiency of Si and InGaAs avalanche photo diode (APD) materials to be above 98% by building an efficient compound detector, commercially available devices have efficiencies ranging between 15 and 75%. This means bandwidth, dark current, cost, and other factors are more important than quantum efficiency for existing applications. For non-classical correlated photon applications, the system's correlated signal-to-noise ratio is proportional to (ηN)^½ /(1 ? η)^½, rather than the classical signal-to-noise (ηN)^½. Consequently, the detector design trade space must be re-evaluated. This paper systematically examines the generic detection process, lays out the considerations needed for designing detectors for non-classical applications, and identifies the ultimate physical limits on quantum efficiency.     

Avalanche photodiodes and quenching circuits for single-photon detection

Avalanche photodiodes, which operate above the breakdown voltage in Geiger mode connected with avalanche-quenching circuits, can be used to detect single photons and are therefore called singlephoton avalanche diodes SPAD's. Circuit configurations suitable for this operation mode are critically analyzed and their relative merits in photon counting and timing applications are assessed. Simple passive-quenching circuits (PQC's), which are useful for SPAD device testing and selection, have fairly limited application. Suitably designed active-quenching circuits (AQC's) make it possible to exploit the best performance of SPAD's. Thick silicon SPAD's that operate at high voltages (250-450 V) have photon detection efficiency higher than 50% from 540- to 850-nm wavelength and still ~3% at 1064 nm. Thin silicon SPAD's that operate at low voltages (10-50 V) have 45% efficiency at 500 nm, declining to 10% at 830 nm and to as little as 0.1% at 1064 nm. The time resolution achieved in photon timing is 20 ps FWHM with thin SPAD's; it ranges from 350 to 150 ps FWHM with thick SPAD's. The achieved minimum counting dead time and maximum counting rate are 40 ns and 10 Mcps with thick silicon SPAD's, 10 ns and 40 Mcps with thin SPAD's. Germanium and III-V compound semiconductor SPAD's extend the range of photon-counting techniques in the near-infrared region to at least 1600-nm wavelength.     

Recent achievements in single photon detectors and their applications

Abstract

Solid state single photon detectors are receiving more and more attention in a number of areas of applied physics: optical sensors, communications, quantum cryptography, optical ranging and Lidar, time resolved spectroscopy, opaque media imaging and ballistic photon identification. This paper reports on results of research and development in the field of solid state single photon detectors at the Czech Technical University in Prague over the last 20 years. Avalanche photodiodes specifically designed for single photon counting devices have been developed based on various semiconductor materials: Si, Ge, GaP, GaAs and InGaAs. Electronic circuits for biasing, quenching and control of these detectors have been developed and optimized for different applications. The sensitivity of solid state photon counters spans from 0.1 nanometre X-rays up to 1800 nanometres in the near infrared region. Timing resolution of solid state photon counters as high as 50 picoseconds full width at a half maximum has been achieved when detecting single photon signals. Circuits permitting operation of solid state photon counters in both single and multiple photon signal regimes have been developed and applied. The compact and rugged design, radiation resistance, and low operating voltage are attractive features of solid state photon counters in various space projects.     

Lucky-drift model for impact ionization in amorphous semiconductors

A lucky-drift model for impact ionization has been recently successfully used to account for avalanche phenomenon in amorphous selenium (a-Se). We extend the calculations in order to compare the effect in a-Se with possible impact ionization phenomenon in another prototype amorphous semiconductor: hydrogenated amorphous silicon (a-Si:H). The results suggest that the higher phonon energy in a-Si:H as compared to a-Se shifts the threshold field for impact ionization in a-Si:H to essentially higher fields than those needed for avalanche multiplication in a-Se. Furthermore, it has been recently suggested that impact ionization is a precursor of the switching effect in the phase-change-memory materials (Ge₂Sb₂Te₅). We apply the lucky-drift model to Ge₂Sb₂Te₅ and show that it is capable to account for the magnitude of the electric field necessary to launch the electronic switching in this material.     

Photon counting at telecom wavelengths with commercial InGaAs/InP avalanche photodiodes: Current performance

Abstract

InGaAs/InP avalanche photodiodes operated in the so-called Geiger mode currently represent the best solution to detect single-photon beyond 900nm. They cover the 1100–1650nm wavelength interval, which includes in particular the two windows used for optical communications (1310 and 1550nm). A detection efficiency at 1550nm of 10% with a dark count probability of 10^?5 ns^?1 is common, although significant variations can be encountered. At this efficiency, a FWHM temporal response of 300 ps can be achieved. Afterpulses caused by charges trapped by defects in the high field region of the junction constitute the main performance impairment phenomenon. They enhance the dark count probability and reduce out-of-gate detector blindness. These photon counting detectors can be used in optical time-domain reflectometry to improve the spatial resolution and reduce dead-zone effects. Quantum key distribution over metropolitan area networks also constitutes an important application.     

The spectral resolution of high temperature GaAs photon counting soft X-ray photodiodes

Circular mesa GaAs p⁺-i-n⁺ diodes for photon counting soft X-ray spectroscopy have been fabricated and characterised over a temperature range of +80 to -30 °C. The spectroscopic performance of the diodes, as measured by the FWHM of the Mn K_α X-ray line from an ⁵⁵Fe radioisotope, is reported. In addition, we compare the GaAs diodes with previously fabricated and characterised Al_0.8Ga_0.2As p⁺-i-n⁺ diodes of similar geometry.     

Avalanche Carrier Multiplication in Multilayer Black Phosphorus and Avalanche Photodetector

A highly sensitive avalanche photodetector (APD) is fabricated by utilizing the avalanche multiplication mechanism in black phosphorus (BP), where a strong avalanche multiplication of electron–hole pairs is observed. Owing to the small bandgap (0.33 eV) of the multilayer BP, the carrier multiplication occurs at a significantly lower electric field than those of other 2D semiconductor materials. In order to further enhance the quantum efficiency and increase the signal‐to‐noise (S/N) ratio, Au nanoparticles (NPs) are integrated on the BP surface, which improves the light absorption by plasmonic effects. The BP–Au‐NPs structure effectively reduces both dark current (≈10 times lower) and onset of avalanche electric field, leading to higher carrier multiplication, photogain, quantum efficiency, and S/N ratio. For the BP–Au‐NPs APD, it is obtained that the external quantum efficiency (EQE) is 382 and the responsivity is 160 A W^‐1 at an electric field of 5 kV cm^‐1 (V_d ≈ 3.5 V, note that for the BP APD, EQE = 4.77 and responsivity = 2 A W^‐1 obtained at the same electric field). The significantly increased performance of the BP APD is promising for low‐power‐consumption, high‐sensitivity, and low‐noise photodevice applications, which can enable high‐performance optical communication and imaging systems.     

Subnanosecond impact-ionization switching of silicon structures without <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">n</Emphasis> junctions

It is shown that an application of a fast-rising high-voltage pulse to an n ⁺–n–n ⁺ silicon structure leads to subnanosecond avalanche breakdown, generation of electron–hole plasma throughout the entire structure, and structure switching to the conducting state in a time of about 100 ps. The predicted effect is similar to the delayed avalanche breakdown of reverse-biased p ⁺–n–n ⁺ diode structures; however, it is implemented in a structure without p–n junctions.     

A.C. electrical breakdown in thin magnesium oxide films

A systematic study of a.c. breakdown in magnesium oxide films of thickness 40–200 Å fabricated into capacitors is reported. It is found that the breakdown strength is a power function of the thickness d, varying as d^?0.23, as predicted by the theory of Forlani and Minnaja based on the ionization avalanche mechanism.     

Dielectric breakdown study of thin La2O3 films

The dielectric breakdown in La₂O₃ films of thickness 40–400 Å incorporated in capacitors is reported. The experimental results were analysed in the light of Forlani and Minnaja's theory of ionization avalanche breakdown. The dielectric breakdown strength was found to be a power function of thickness, varying as d^?0.66, in essential agreement with the theory of Forlani and Minnaja. Furthermore, these films are amorphous and have high breakdown fields (about 10 MV cm^?1).     

High efficiency single photon detection via frequency up-conversion

Abstract

We propose a method of single photon detection of infrared (IR) photons at potentially higher efficiencies and lower noise than allowed by traditional IR band avalanche photodiodes (APDs). By up-converting the photon from the IR, e.g. 1550 nm, to a visible wavelength in a nonlinear crystal, we can utilize the much higher efficiency of silicon APDs at these wavelengths. We have used a periodically poled lithium niobate (PPLN) crystal and a pulsed 1064 nm Nd:YAG laser to perform the up-conversion to a 631 nm photon. We observed conversion efficiencies as high as ～ 80%, and demonstrated scaling down to the single photon level while maintaining a background of 3 ×s; 10^?4 dark counts per count. We also propose a 2-crystal extension of this scheme, whereby orthogonal polarizations may be up-converted coherently, thus enabling complete quantum state transduction of arbitrary states.     

14 MHz rate photon counting with room temperature InGaAs/InP avalanche photodiodes

Abstract

We have developed high speed gated-mode single-photon counters based on InGaAs/InP avalanche photodiodes for use at 1.55 μm wavelength. Operation at room temperature allows afterpulse probability to be below 0.2% for gate rates up to 14 MHz. We obtained optimum noise-equivalent power of 2.2 ×s; 10^?15 W Hz^?1/2 at 14% quantum efficiency with dark-count probability of 0.2%. We propose a metric (noise-equivalent power divided by gate frequency) for comparing high speed photon counters and show that for this metric our system outperforms previously reported counters at 1.55 μm wavelength. We demonstrate that for gate widths of a nanosecond or below, the differing amplitude distributions of dark versus light counts allow an optimal decision threshold to be set for a given bias voltage.     

Parameters of silicon carbide diode avalanche shapers for the picosecond range

Parameters of ultrafast avalanche switching of high-voltage diode structures based on 4H-SiC have been estimated theoretically. The calculation was carried out using the analytical theory of the impact ionization wave of the TRAPATT type, which makes it possible to determine the main characteristics of a wave for arbitrary dependences of the impact ionization coefficients and carrier drift velocity on electric field. It is shown that, for a high-voltage (1–10 kV) 4H-SiC structure, the time of switching from the blocking to the conducting state is ~10 ps, which is an order of magnitude shorter than that for a Si structure with the same stationary breakdown voltage, and the concentration of the electron-hole plasma created by the wave is two orders of magnitude higher. Picosecond switching times can be reached for 4H-SiC structures with a stationary breakdown voltage exceeding 10 kV.     

Numerical simulation of spatially nonuniform switching in silicon avalanche sharpening diodes

The process of spatially nonuniform switching in high-voltage silicon diodes operating in the delayed avalanche regime has been numerically simulated. The dependence of the transient process on the ratio between the total diode cross-section area and the area of the region where the switching takes place has been studied. The switching time (60?C70 ps) and qualitative form of the transient characteristic agree with the available experimental data. It is established that a rapid drop of the diode voltage begins after the ionization front has traveled over most of the base and then continues due to secondary avalanche breakdown of the base filled with free carriers. Thus the time of switching to the conducting state exhibits no direct correlation with the velocity of ionization front propagation.