Low Reverse Bias Voltage Research Articles

High responsivity and wide bandwidth operation of InP-based pin-photodiode array monolithically integrated with 90° hybrid using butt-joint regrowth

The InP-based pin-photodiode array monolithically integrated with a 90° hybrid consisting of multimode interference structures was fabricated using the butt-joint regrowth for compact 100 Gbps coherent receivers. The low dark current of less than 0.2 nA was obtained with InP passivation effect through the selective regrowth process in four-channel photodiodes. A responsivity including total loss of 8.3 dB in the waveguide was as high as 0.14 A/W. The wide 3 dB bandwidth of 24 GHz at a low reverse bias voltage of 1.6 V was also achieved under high optical input power conditions (photocurrent: 4 mA).

Deep-level traps induced dark currents in extended wavelength InxGa1−xAs/InP photodetector

The dark current mechanism of extended wavelength InxGa1−xAs photo-detectors is still a debated issue. In this paper, the deep-level transient spectroscopy (DLTS) and dark current characteristics of InxGa1−xAs/InP detectors are investigated. Using trap parameters obtained from DLTS measurement, the device simulations of current-voltage characteristics are carried out by Silvaco Altas. The results reveal that the dark current at the low reverse bias voltage is associated with deep level trap induced trap assisted tunneling and Shockley-Read-Hall generation mechanism. The reduction of the deep level trap concentration in InxGa1−xAs absorption layer could dramatically suppress the dark current near zero bias in extended wavelength InxGa1−xAs/InP detectors.

Polarization effects on gate leakage in InAlN/AlN/GaN high-electron-mobility transistors

Lattice-matched InAlN/AlN/GaN high electron mobility transistors offer high performance with attractive electronic and thermal properties. For high-voltage applications, gate leakage currents under reverse bias voltages remain a serious challenge. This current flow is dominated by field enhanced thermal emission from trap states or direct tunneling. We experimentally measure reverse-bias gate leakage currents in InAlN/AlN/GaN transistors at various temperatures and find that the conventional trap-assisted Frenkel-Poole model fails to explain the experimental data. Unlike the non-polar semiconductors Si, Ge, large polarization-induced electric fields exist in III-nitride heterojunctions. When the large polarization fields are accounted for, a modified Frenkel-Poole model is found to accurately explain the measured data at low reverse bias voltages. At high reverse bias voltages, we identify that the direct Fowler-Nordheim tunneling mechanism dominates. The accurate identification of the gate leakage current flow mechanism in these structures leads to the extraction of several useful physical parameters, highlights the importance of polarization fields, and leads to suggestions for improved behavior.

Color separation enhancement of pixn diodes by optimizing absorption regions of a-SiGe:H/a-SiC:H alloys and using a low reflective Al-doped ZnO cathode

ABSTRACTSecurity imaging systems working with crystalline silicon CCD or CMOS detectors are not able to distinguish colorimetrically between a large number of dangerous chemical substances, for example whitish powders [1]. In order to offer an alternative to expensive and destructive chemical methods of analysis, we developed optimized hydrogenated amorphous silicon (a-Si:H) multicolor photodiodes with different spectral response characteristics for a reliable, fast, cheap and non-destructive identification of potentially dangerous substances. Experimental optical, C-V and I-V studies were performed to explore the effect of combining linear graded a‑SiC:H-/a‑SiGe:H layers with low-reflective ZnO:Al back-contacts. Typically, a-Si:H with profiled energy gaps can be found in tandem solar cells to optimize the collection of incoming photons [2,3]. We determined the absorption coefficients of a group of a-SiC:H and a-SiGe:H graded and non-graded layers to calculate the penetration depth of photons at different energies into the device structure. Knowing the indices of absorption, refraction and extinction, it is possible to engineer diodes in such a way that accumulations of charge carriers are generated precisely at varying device depths. Common chromium back reflectors avoid a sharp falling edge of the sensitivity towards longer wavelengths and lead to interference fringes in the spectral response [4]. By combining linear graded absorption zones and ZnO:Al back contacts, we designed an optimized device with a highly precise adjustment of the spectral sensitivity reaching from 420 nm to 560 nm and reduced interference fringes at a very low reverse bias voltage of maximum -2.5 V. Similar three terminal devices allow a shift from 440 nm to 630 nm, however, at a much higher reverse bias of -11 V at 560 nm [4]. Present research efforts concentrate on the development of fast and high dynamic front illumination device structures which ensure a continuous narrow-band shift of the spectral photosensitivity and an optimum adaption to a predetermined light source-/sample measurement configuration.

Effect of threading defects on InGaN∕GaN multiple quantum well light emitting diodes

Photoelectrochemical etching was used to measure the threading defect (TD) density in InGaN multiple quantum well light-emitting diodes (LEDs) fabricated from commercial quality epitaxial wafers. The TD density was measured in the LED active region and then correlated with the previously measured characteristics of these LEDs. It was found that the reverse leakage current increased exponentially with TD density. The temperature dependence of this dislocation-related leakage current was consistent with a hopping mechanism at low reverse-bias voltage and Poole-Frenkel emission at higher reverse-bias voltage. The peak intensity and spectral width of the LED electroluminescence were found to be only weakly dependent on TD density for the measured TD range of 1×107–2×108cm−2.

Defect-induced trap-assisted tunneling current in GaInNAs grown on GaAs substrate

We present the reverse-bias current-voltage and deep-level transient spectroscopy (DLTS) characteristics of a Ga0.90In0.10N0.033As0.967∕GaAs positive-intrinsic-negative photodiode (Eg=0.92 eV) and a trap-assisted tunneling model which considers generation-recombination and tunneling mechanisms. Using trap parameters obtained from the DLTS measurement, the model generates current-voltage characteristics of the photodiode, which were found to be in good agreement with experimental current-voltage curves at different temperature. The model also suggests that high dark current at low reverse-bias voltage is caused by the presence of traps which have low activation energy. Furthermore, it is predicted that approximately ten times reduction in the dark current can be achieved when the trap concentration of type H-1 (Ea=0.15 eV) is reduced by one order. On the other hand, a similar reduction in defect concentration of type H-2 (Ea=0.40 eV), which is nearer to midgap does not produce the same effect.

High-Power Ultralow-Chirp 10-Gb/s Electroabsorption Modulator Integrated Laser With Ultrashort Photocarrier Lifetime

A high-power, ultralow-chirp electroabsorption modulator (EAM) integrated with a distributed-feedback laser diode (EML) having ultrashort lifetime of photogenerated holes in the EAM quantum-well (QW) structure is reported for the first time. A shallow QW structure having a small valence band offset to enhance the sweepout of photogenerated holes was employed as EAM absorption layer. The measured hole lifetimes were 7-11 ps, and the measured frequency chirp (/spl alpha/-parameter) was low or negative at low EAM reverse bias voltages even under high optical output power conditions. Successful 10-Gb/s 80-km normal-dispersion single-mode fiber transmission (chromatic dispersion D=1600 ps/nm) and the record average fiber optical output power (P/sub f/) of +5.3 dBm were achieved at 25/spl deg/C. In addition, semicooled operation of EML at enhanced bit rates has been demonstrated for application in small-form-factor protocol-agnostic optical transceivers. A 10.7-Gb/s 1600-ps/nm transmission was achieved at 45/spl deg/C and P/sub f/=+3.0 dBm.

Room-temperature gas-sensing ability of PtSi/porous Si Schottky junctions

Gas-sensing ability of n-type PtSi/porous Si Schottky junctions is investigated at room temperature. These junctions exhibit a breakdown-type current-voltage (I-V) curve at low reverse bias voltages (5-15 V) due to very large electric fringing fields (10/sup 5/-10/sup 6/ V/cm) developed at the sharp edges and the bottom of the pores. Experimental results for selected gases are presented. Gases with inherent dipole moments tend to decrease the breakdown voltage. Gases without dipole moments do not affect the I-V curve directly, but they can replace gas content inside the pores and decrease the dipole moment of the ambient gas, which results in an increase in breakdown voltage. Based on these experiments, the possible application of this structure as a gas sensor at room temperature is discussed.

Two-dimensional a-Si:H/a-SiC:H n-i-p sensor array with ITO/a-SiNx antireflection coating

AbstractThis paper presents a two-dimensional a–Si:H/a-SiC:H n–i–p photodiode array with switching diode readout, developed specifically for fluorescence-based bio-assays. Both device structure and fabrication processing has enabled enhancement of the external quantum efficiency of the encapsulated device up to 80%, reduction of the photodiode leakage down to 10 pA/cm2 at -1V reverse bias, and increase of the rectification current ratio of the switching diodes up to 109. The critical fabrication issues associated with deposition of device-quality materials, tailoring of defects at the i–p interface, device patterning with dry etching, junction passivation, and contact formation will be discussed. Both sensing and switching diodes were characterized. While the observed dark current in the photodiodes at low reverse bias voltages is primarily due to carrier emission from deep states in the a–Si:H bulk, the leakage in the small switching diodes stems from peripheral defects along junction sidewalls. Optical losses in the photodiodes with ITO/a–SiNx:H antireflection coating were evaluated using numerical modeling, and the calculated transmission spectra correlated well with the spectral response characteristics. Measurements of the charge transfer time and output linearity demonstrated the efficiency of the single-switching diode readout configuration. The response of the array to optical excitation was also investigated. The observed long term retardation in the signal rise and decay at illumination levels less than 1010 photons/cm2-s can be associated with charge trapping in the undoped layer.

Optical gain at low bias voltages in electrostatic-discharge-damaged silicon p-i-n photodiodes

Abstract The sensitivity of commercial p-i-n silicon photodiodes to electrostatic discharges was determined by monitoring continuously electronic and optoelectronic device properties during human body model step-stress tests. The device degradation threshold pulse amplitudes ranging from 175 to 300 V for reverse-bias stress and from 10000 to 13 500V for forward-bias stress were found, evidenced in all cases by an increase in the reverse-bias dark current. In the case of a forward-bias-stressed diode, however, we observed a substantial increase in the responsivity of the photodiode at low reverse-bias voltages after electrostatic-discharge-related degradation. The photocurrent gain, which increased with decreasing light intensity and increasing bias voltage, reached a saturation value exceeding 500 for low optical powers and a reverse-bias voltage of 10 V. Additionally it was observed than the open-circuit voltage of the photodiode at a given light power is a more sensitive parameter for device degradation...

Optical gain at low bias voltages in electrostatic-discharge-damaged silicon p-i-n photodiodes

Abstract The sensitivity of commercial p-i-n silicon photodiodes to electrostatic discharges was determined by monitoring continuously electronic and optoelectronic device properties during human body model step-stress tests. The device degradation threshold pulse amplitudes ranging from 175 to 300 V for reverse-bias stress and from 10000 to 13 500V for forward-bias stress were found, evidenced in all cases by an increase in the reverse-bias dark current. In the case of a forward-bias-stressed diode, however, we observed a substantial increase in the responsivity of the photodiode at low reverse-bias voltages after electrostatic-discharge-related degradation. The photocurrent gain, which increased with decreasing light intensity and increasing bias voltage, reached a saturation value exceeding 500 for low optical powers and a reverse-bias voltage of 10 V. Additionally it was observed than the open-circuit voltage of the photodiode at a given light power is a more sensitive parameter for device degradation than the reverse-bias dark current and the short-circuit current.

Surface and bulk leakage currents in high breakdown GaN rectifiers

GaN Schottky diode rectifiers with contact diameters 125–1100 μm were fabricated on thick (4 μm) epi layers. At low reverse bias voltages the leakage current was proportional to contact perimeter size while at voltages approximately half the breakdown value, the reverse current was proportional to contact area. These results suggest that surface leakage dominated at low biases, while at higher biases the main contribution was from bulk leakage. The reverse leakage currents were several orders of magnitude higher than the theoretical values, while the forward turn-on voltages were approximately a factor of two higher than the theoretical value.

Simultaneous analysis of current–voltage and capacitance–voltage characteristics of metal–insulator–semiconductor diodes with a high mid-gap trap density

We present an improved method to analyze simultaneously the current–voltage and capacitance–voltage characteristics of metal–insulator–semiconductor (MIS) diodes. We use the method to study the effect of Zn doping concentration on the current transport in Au MIS contacts fabricated on In0.21Ga0.79As layers grown by metalorganic vapor phase epitaxy on highly doped GaAs substrates. At room temperature and for low reverse bias voltage, the generation/recombination process via mid-gap traps is the only dominant mechanism in these MIS diodes. For high reverse bias, both this mechanism and thermionic-field emission control current transport. The generation/recombination current observed is due to donor type mid-gap traps whose density shows an almost linear dependence with Zn concentration. The value of the barrier height at zero bias and at room temperature (φb0=0.73 V±12%) is independent of the Zn concentration. For the procedure used to prepare the In0.21Ga0.79As:Zn surfaces, the thickness of the oxide layer and the transmission coefficient of holes across this layer depend on the Zn doping concentration in the range 7×1014⩽NA⩽5×1018 cm−3. Zn doping seems to inhibit the formation of the unintentional native oxide on the surface of In0.21Ga0.79As epilayers.

InP-InGaAs uni-traveling-carrier photodiode with improved 3-dB bandwidth of over 150 GHz

Uni-traveling-carrier photodiodes (UTC-PD's) with ultrafast response and high-saturation output are reported. It is experimentally demonstrated that the photoresponse of UTC-PD's is improved by incorporating a step-like potential profile in the photoabsorption layer. The fabricated device shows a peak electrical 3-dB bandwidth of 152 GHz at a low reverse bias voltage of -1.5 V. The output voltage can be increased to as high as 1.9 V at higher reverse bias voltages with the 3-dB bandwidth staying at over three-quarters of the maximum value. To our knowledge, the obtained response is the fastest among those reported for 1.55-/spl mu/m wavelength photodiodes.

The operational principle of a new amorphous silicon based p-i-i-n color detector

The operational principle of a new type p-i-i-n color sensor is described with the aid of numerical modeling. The modeling results account for the color detection mechanism recently presented that this kind of structure exhibits [T. Neidlinger, M. B. Schubert, G. Schmid, and H. Brummack, in Amorphous Silicon Technology—1996, edited by E. A. Schiff et al. (Materials Research Society, Pittsburgh, 1996), p. 147]. By band gap engineering the experimental red response is maximized at larger reverse bias voltage whereas the green response has its maximum at low reverse bias voltage. The numerical modeling qualitatively reproduces the characteristic shape of the steady-state current-voltage curves at different illumination wavelengths. At low and at high reverse bias voltages the influence of the internal variables and parameters is identified and leads to the experimentally observed response. The potential profile of the p-i-i-n structure is of crucial importance to the color detection mechanism. At larger wavelengths the large potential drop across the two highly defective front layers assists recombination in the back part of the device, which thus leads to the drop in the red response at low reverse voltage. For the voltage-dependent shift in spectral sensitivity it is important that photogenerated carriers under green bias illumination are lost by recombination in the front part of the device.

Microdischarges of AC-coupled silicon strip sensors

Microdischarge at the edges of strips in AC-coupled silicon strip sensors has been investigated. A steep increase in the leakage current (breakdown) and a sudden onset of burst noise were observed at a low reverse-bias voltage when the bias potential was across the AC-coupling capacitor. This can be explained by the occurrence of microdischarges along the edges of strips. These discharges have been confirmed by observing IR light emission. A calculation of the field strength at the strip edge suggests that a fringe field of the external electrode generates the microdischarge at the strip edge when the bias voltage is 50–80 V. This is consistent with our observations. We discuss a design for AC-coupled sensors that eliminates this discharge problem.

External bias voltage and incident light intensity dependent effects of quantum-confined excitonic transitions on bulk background photocurrent spectra

An experimental investigation of the unique photocurrent spectra of p-i-n photodiode with a GaAs/AlAs/AlGaAs quantum well and bulk GaAs absorption regions at 77 K is presented. The results showed that the excitonic absorption transitions in the quantum wells create sharp dips in the featureless bulk background spectra for low reverse bias voltages, while the spectra at high reverse biases show normally expected features with sharp quantum-confined excitonic absorption peaks superimposed on the background absorption. Furthermore, we found that the spectral features are very sensitive to the incident light intensity. These remarkable results are explained in terms of competition between the carrier escape rate from the quantum well region and the carrier generation rate in the bulk GaAs region, as well as by partial screening induced by carriers accumulated in the quantum well region.

Reverse I-V characteristics in Au-GaAs Schottky diode in the presence of interfacial layer

The existence of an interfacial layer in an Au-GaAs Schottky diode may be revealed by measuring its I-V characteristics at very low reverse bias voltage. It is shown in this letter that a voltage dividing factor m can be used [see (2) of the text] to describe the effect of the interfacial layer on the I-V characteristics of the diode at low bias voltage.

Voltage controlled minority carrier collection—the exponentially retrograded photodiode

The large retarding field in an exponentially retrograded photodiode is shown to significantly reduce the base-generated photocurrent at low reverse-bias voltages. Increasing the reverse voltage on the diode reduces the length over which this retarding field is effective, thereby increasing the Photo-Transmission Coefficient of the diode. From avalanche breakdown considerations, the largest ratio of change in photocurrent caused by this effect is shown to be only a function of the resistivity and bulk-lifetime in the base of the diode. This voltage-controlled collection effect is observable only in diodes with high background resistivity (i.e. ϱ silicon > 25 Ω cm.). It is theoretically possible to obtain voltage-controlled collection ratios of better than 50:1 in, typically, a 10 V junction swing. Experimental results compare well with theoretical models.