Junction Electric Field Research Articles

Deep level transient spectroscopy characterisation of defects in AlGaN/Si dual‐band (UV/IR) detectors grown by MBE

AbstractThis paper is based on the investigation of electrically active defects in dual band UV/IR photodiodes using Deep Level Transient Spectroscopy (DLTS). The UV/IR photodiodes were fabricated by growing Al0.7Ga0.3N layers on silicon substrate to obtain UV‐ sensitive photodiode structures on the front side, whereas on the back side of silicon IR‐sensitive photodiode structures were fabricated. Our studies reveal the existence of two defect levels in each detector. In order to determine accurately the position of these levels within the band gap of the respective layers, Laplace DLTS has been employed. The activation energies of defects in the UV photodetectors are 0.11±0.01 eV, and 0.31±0.01 eV, whereas, those in the IR detector are 0.25±0.01 eV and 0.47±0.02 eV. These energies are with respect to the conduction band energy of each detector. The effect of the junction electric field on the carrier emission rates of the deep traps was investigated by applying the double pulse Laplace DLTS technique. In particular it is found that the activation energy of the defect in the IR detector (0.47±0.02 eV) changes with electric field. Therefore, in this paper we will present detailed DLTS and Laplace DLTS investigations of deep traps in detectors based on AlGaN/Si (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier depletion and exciton diffusion in a single ZnO nanowire

Carrier depletion and transport in a single ZnO nanowire Schottky device havebeen investigated at 5 K, using cathodoluminescence measurements. An excitondiffusion length of 200 nm has been determined along the nanowire axis. Thedepletion width is found to increase linearly with the reverse bias. The origin of thisunusual dependence in semiconductor material is discussed in terms of chargelocation and dimensional effects on the screening of the junction electric field.

Wide bandgap n-type and p-type semiconductor porous junction devices as photovoltaic cells

In junction absorber photovoltaics doped wide bandgap n-type and p-type semiconductors form a porous interpenetrating junction structure with a layer of low bandgap absorber at the interface. The doping concentration is high enough such that the junction depletion width is smaller than the pore size. The highly conductive neutral region then has a dentrite shape with fingers reaching the absorber to effectively collect the photo-carriers swept out by the junction electric field. With doping of 1019 cm−3 corresponding to a depletion width of 25 nm, pore size of 32 nm, absorber thickness close to exciton diffusion length of 17 nm, absorber bandgap of 1.4 eV and carrier mobility over 10−5 cm2 V−1 s−1, numerical calculation shows the power conversion efficiency is as high as 19.4%. It rises to 23% for a triplet exciton absorber.

Effects of irradiation and annealing on deep levels in rhodium-doped p-GaAs grown by metal-organic chemical-vapor deposition

This paper reports a detailed study of the effects of irradiation and thermal annealing on deep levels in Rh-doped p-type GaAs grown by low-pressure metal-organic chemical-vapor deposition, using deep level transient spectroscopy (DLTS) technique. It is found upon irradiation with alpha particles that, in addition to the radiation-induced defect peaks, all the Rh-related peaks observed in majority, as well as minority-carrier emission DLTS scans show an increase in their respective concentrations. The usually observed α-induced defects Hα1, Hα2, and Hα3 are found to have lower introduction rates in Rh-doped samples, as compared to reference samples (not doped with Rh). Alpha-irradiation has been found to decompose the two minority carrier emitting bands (one at low temperature ∼150 K and the other at ∼380 K) observed prior to irradiation into distinct peaks corresponding to deep levels Rh1 and Rh2 and EL2 and Rh3, respectively. A similar effect is also observed for the majority-carrier emitting band composed of hole emission from deep levels RhA and RhB, which separate out well upon irradiation. Further, from the double-correlation DLTS measurements, the emission rates of carriers from the radiation-enhanced peaks corresponding to deep levels Rh1, Rh2, Rh3, and RhC were found to be dependent on junction electric field. For RhC, the field dependence data have been analyzed in terms of the Poole-Frenkel model employing a 3-dimensional Coulomb potential with q = 2e (electronic charge). Temperature dependence of the hole capture cross-sections of the levels RhA and RhC was also studied quantitatively. The observed dependence of the hole capture cross-section of RhC on temperature can be interpreted in terms of multiphonon capture model, yielding a capture barrier of 0.2 eV and σ(∞) = 2.3 × 10−14 cm2. The results of irradiation and isochronal thermal annealing study, in combination with the theoretical analysis of the field dependence of hole emission data, lead us to interpret the levels RhA and RhB as charged centers and probably complexes of arsenic anti-site defect (AsGa) with Rh-impurity, (AsGa-Rh). The levels Rh1 and Rh2 are also proposed to be complexes, albeit of a different type, of arsenic anti-site defects (AsGa) and Rh-impurity (AsGa-Rh), while the level RhC is likely to be a doubly-charged complex center composed of arsenic interstitial (IAs) and Rh-impurity (IAs-Rh).

Improvement in Junction Breakdown and GIDL using MFLA in DRAM Product

In this study, we successfully improved junction breakdown using millisecond flash anneal (MFLA) on a dynamic random access memory (DRAM) product. By replacing a rapid thermal annealing (RTA) process with MFLA after contact implantation, improvements in NMOS and PMOS junctions were observed and no degradation was found. Device simulation data show that the PMOS junction electric field (E-field) was reduced with MFLA and that MFLA has an advantage in junction profile tailoring. The behavior of gate-induced drain leakage (GIDL) at different process stages with different annealing temperatures was studied. The preheat and peak temperatures of MFLA were found to be correlated with GIDL improvement. The optimum condition in this study was 1200°C flash anneal with a 750°C preheat temperature. Bright field and weak-beam dark-field transmission electron microscopy images showed perfect dislocation loops and fault dislocation loops remaining in the {113} plane with a size of around 17 × 20 nm in the junction area.

Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV.

Shallow trench isolation stress modification by optimal shallow trench isolation process for sub-65-nm low power complementary metal oxide semiconductor technology

Shallow trench isolation (STI) induced mechanical stress affects the device behavior in the advanced complementary metal oxide semiconductor (CMOS) technology. This article presents how to use an optimal STI process to reduce transistor mismatch and leakage current induced standby current in static random access memory (SRAM). The STI induced mechanical stress affects the device behavior in the advanced CMOS technology. The optimized STI process can reduce junction and bulk leakage that occurs on the STI sidewall due to STI compressive stress enhancing boron diffusion and increasing junction electric field of STI sidewall resulting in band-to-band-tunneling (BTBT) degradation. An obvious decrease in BTBT occurs on STI edge sidewall that is observed by using the optimized STI process. Meanwhile, the optimized STI process has better length of diffusion effect. Moreover, the optimized STI process can improve the parasitic device at STI edge because of smaller divot. Since random fluctuation of channel dopant and process induced device mismatch are major considerations in SRAM cell, we examine STI sidewall boron dopant diffusion effect on SRAM due to BTBT increasing exponentially with increasing doping concentration in the P-well of negative metal oxide semiconductor field effect transistor. The mismatch of passing gate of SRAM and Vcc_min can also be improved by leakage reduction from the optimized STI process due to improved random dopant fluctuation.

Arsenic antisite defects in p-GaAs grown by metal-organic chemical-vapor deposition and the EL2 defect

Epitaxial layers of p-GaAs grown on p+-GaAs substrates by low-pressure metal organic chemical vapor deposition have been investigated using deep level transient spectroscopy (DLTS). One dominant peak and other relatively small peak, corresponding to deep levels at Ev+0.55 eV and Ev+0.96 (low field energies), respectively, have been observed in the lower half of the band gap. Investigation with double-correlation DLTS reveals that the measured thermal emission rate of holes from the dominant level is strongly dependent on the junction electric field. Detailed data on this field enhancement have been analyzed in terms of different available theoretical models. The hole capture cross section for the dominant deep level has been found to be temperature dependent. Detailed data on the temperature dependence of the hole capture cross section have been interpreted in terms of the multiphonon carrier capture mechanism, yielding a capture barrier of 0.11 eV. In order to get deeper insight into the nature and origin of these inadvertent (intrinsic) defects, thermal annealing behavior of these levels has also been studied. Analyses of field dependence and hole capture data, in combination with the annealing study, suggest that the dominant level is associated with an arsenic-antisite (AsGa) defect. Probable association of this dominant level with the doubly charged state of the well-known EL2 defect has been discussed in detail.

Fully-depleted Ge interband tunnel transistor: Modeling and junction formation

Complementary fully-depleted Ge interband-tunneling field-effect transistors (TFETs) and static inverters are modeled to quantify TFET performance relative to Si MOSFETs. SYNOPSYS TCAD is used to compute the two-dimensional electrostatics and determine the tunnel junction electric field. This electric field is used in an analytic expression to compute the tunnel current. The speed and power performance of TFETs are compared with the nMOSFET at the same supply voltage, 0.5 V. For a gate length of 20 nm, Ge tunnel transistors can provide similar speed in comparison to 45-nm-node nMOSFETs (18 nm gate length), but saves more than 2× in power and lowers energy by over 7×. Toward demonstrating these transistors, a process for forming submicron p +n + Ge tunnel junctions has been utilized in which Al-doped p + Ge is regrown on n + Ge, following melt-back of a patterned Al deposition. Transmission electron microscopy (TEM) reveals the regrown film and a contact microstructure consistent with the Al–Ge phase diagram. The low peak-to-valley current ratio (PVR) of devices produced by this growth method is likely a result of point defects or junction doping non-uniformity as TEM suggest no dislocations at the regrown junction. The PVR of these junctions does not improve as the device area is reduced from 100 to 0.1 μm 2, a size smaller than the formation scale for grains in the Al–Ge system.

Extreme UV photodetectors based on CVD single crystal diamond in a p-type/intrinsic/metal configuration

We report on extreme UV (EUV) photodetectors based on CVD single crystal diamond in a p-type/intrinsic/metal configuration fabricated and tested at Roma “Tor Vergata” University laboratory, operating in a sandwich geometry. Particular care has been devoted to the design of the device geometry in order to take advantage of the internal junction electric field and to minimize the signal contribution arising from secondary electron emission, which is known to strongly affect the detection properties in the UV and EUV regions. The device has been characterized in the EUV spectral region by using both He and He–Ne DC gas discharge radiation sources and a toroidal grating vacuum monochromator, with 5 Å wavelength resolution. The reproducibility test has been performed on several photodetectors showing a high uniformity of the device performances. The devices showed negligible undesired effects such as persistent photocurrent and memory effects, resulting in extremely promising stability features of the p-type/intrinsic/metal structured device. The devices have been tested at different bias voltages between 0 and 15 V, showing the best performances at 0 bias voltage. Finally, the external quantum efficiency (EQE), as well as the responsivity have been measured in the range 20 to 100 nm.

Transverse magnetic field polarity effects on the terahertz radiation from GaAs/AlGaAs modulation-doped heterostructures with varying AlGaAs spacer-layer thickness

We report the effect of changing the polarity of a magnetic field parallel to the surface plane of GaAs/AlGaAs modulation-doped heterostructures (MDHs) with various spacer thicknesses on the terahertz radiation power and its spectral characteristics. Results show that flipping the direction of the transverse 1 T magnetic field modifies the extent of field-induced terahertz radiation enhancement. The observations are analyzed in the context of junction electric field strength, carrier confinement and mobility, and the AlGaAs/GaAs interface roughness. This terahertz method may prove as an efficient tool to qualitatively evaluate the characteristics of MDH layers.

Electrical characterization of alpha radiation-induced defects in p-GaAs grown by metal-organic chemical-vapor deposition

Investigations of the alpha particle irradiation-induced defects in low-pressure metal-organic chemical-vapor deposition grown p-GaAs have been carried out. By employing deep-level transient spectroscopy, at least seven radiation-induced deep-level defects have been observed in the lower half of the band gap in the temperature range of 12−475 K. Double-correlation deep-level transient spectroscopy measurements show three prominent levels: two known radiation-induced levels namely, Hα1 and Hα5, and one inadvertent center HSA, present before irradiation, to exhibit a significant dependence of thermal emission rate on the junction electric field. For Hα1 and HSA the field-enhanced emission data are well fitted with a Poole-Frenkel model, using a three-dimensional square-well potential with radius r=3.2 and 1.43 nm, respectively. The field effect for Hα5 has been explained by a square-well potential in combination with a phonon-assisted tunneling process. Detailed data on the carrier capture cross section for all three levels have been obtained. The hole capture cross section for the levels Hα1 and Hα5 are found to be temperature independent, while for HSA, the hole capture data show a dependence on temperature. The dependence of hole capture cross section of HSA on temperature has been explained in terms of multiphonon capture mechanism, yielding a capture barrier of 0.13 eV and σ(∞)=1.5×10−14 cm2. These analyses lead us to conclude that the levels Hα1 and HSA are associated with a charged center, while the level Hα5 is most likely a substitutional defect in GaAs.

DARK CURRENTS AND IMPACT IONIZATION COEFFICIENTS IN THE InP-InGaAsP DOUBLE HETEROSTRUCTURES

The dependence of reverse-biased leakage current on both voltage and temperature for InP - In x Ga 1-x As y P 1-y DH (double heterostructures) has been analyzed. We find that at the whole of the temperature range and at a wide range of reverse bias voltages, the reverse current varies exponentially with applied voltage, indicating that the band-to-band tunneling current mechanism prevails. An agreement is obtained between theory and experimental results. The tunneling current becomes substantial at peak junction electric fields as low as 105 V/m due to the small direct energy gaps and small effective masses of the structures tested. The process of breakdown in the investigated structures was of the avalanche type. The impact ionization coefficients in In x Ga 1-x As y P 1-y have been experimentally determined for composition x=0.68.

VLWIR HgCdTe detector current-voltage analysis

This article details current-voltage characteristics for a very long wavelength infrared (VLWIR) Hg1−xCdxTe detector from Raytheon Vision Systems with a cutoff wavelength of 20.0 µm at 28 K. In this article, the VLWIR detector diode currents are modeled as a function of bias and temperature. This in-depth current model includes diffusion, band-to-band tunneling, trap-assisted tunneling (TAT), and shunt currents. The trap density has been extracted from the modeled TAT component of the current and was revealed to be relatively temperature-independent. An attempted incorporation of VLWIR detector susceptibility to stress has also been included through variation of the model parameter associated with the p-n junction electric field strength. This field variation accounts for stress induced piezoelectric fields. The current in this VLWIR detector was found to be diffusion-limited under much of the temperature and bias ranges analyzed. This modeling allows the scrutiny of both the dominant current-limiting mechanism and the magnitudes of the various current components as a function of both bias and temperature, allowing the straightforward determination of the ideal operating conditions for a given detector.

Osmium impurity-related deep levels in n-type GaAs

The 5d transition-metal impurity, osmium, has been incorporated during the growth of n-type GaAs epitaxial layers using low-pressure metal-organic chemical-vapor deposition to characterize defect states associated with this heavy and, therefore, thermally stable dopant impurity. Deep-level transient spectroscopy has been employed to investigate the electrical characteristics of Os-related deep levels. Two prominent deep levels have been identified with Os at Ec−0.28eV (Os1) and Ec−0.41eV (Os2) in the upper half-band-gap of GaAs, while no Os-related level has been clearly detected in the lower half-band-gap. The detailed characteristics determined for the two levels include thermal emission rate signatures, leading to the above cited thermal activation energies, electron-capture cross sections, and their temperature dependence, measured by direct pulse-filling technique and deep-level concentrations. Further, both levels are found to exhibit a significant dependence of thermal emission rates on the junction electric field. While Os1 does not allow accurate quantitative investigations of this field dependence due to its relatively low concentration, detailed quantitative data on the field dependence of the level Os2 are reported. Analysis of these data in light of the available theoretical models allows us to conclude that Os2 is probably a substitutional donor-type defect in GaAs.

Gamma radiation induced space charge sign inversion and re-inversion in p-type MCZ Si detectors and in proton-irradiated n-type MCZ Si detectors

Positive space charge build-up was observed in proton—and neutron—irradiated high-resistivity magnetic Czochralski (MCZ) n-type Si detectors after gamma radiation. Space charge sign re-inversion (SCSRI) from negative to positive was achieved at the high dose of 454 Mrad in a low-fluence proton irradiated MCZ Si detector. No SCSRI has been observed yet for low-fluence neutron-irradiated MCZ Si detectors at the highest dose in this study (662 Mrad), but positive space charge is building up, and SCSRI is expected at higher doses. Up to the highest dose in this study, the double junction or double peak electric field distribution is still preserved even after SCSRI. No SCSRI was observed in control FZ Si detectors. Space charge sign inversion was also observed in high-resistivity as-processed MCZ p-type Si detectors after gamma radiation.

Lateral interband tunneling transistor in silicon-on-insulator

We report on a lateral interband tunneling transistor, where the source and drain form a heavily doped lateral pn junction in a thin Si film on a silicon-on-insulator (SOI) substrate. The transistor action results from the control of the reverse-bias tunneling breakdown under drain bias VD by a gate voltage VG. We observe gate control over tunneling drain current ID at both polarities of VG with negligible gate leakage. Systematic ID(VG,VD) measurements, together with numerical device simulations, show that in first approximation ID depends on the maximum junction electric field Fmax(VG,VD). Excellent performance is hence predicted in devices with more abrupt junctions and thinner SOI films. The device does not have an inversion channel and is not subject to scaling rules of standard Si transistors.

Osmium related deep levels in n-type GaAs

Deep levels due to 5d transition metal, osmium (Os), in n-type GaAs epitaxial layers grown by metal-organic vapour-phase epitaxy are investigated using deep level transient spectroscopy (DLTS). Two clear and prominent peaks are observed in majority carrier (electron) emission spectra in GaAs:Os samples in addition to a weaker, broad feature at higher temperatures, which are absent in the Os-free, reference samples. The well-resolved, prominent peaks are attributed to deep levels associated with Os impurity having activation energies Ec−0.28eV and Ec−0.41eV at a junction electric field of ∼1.4×105V/cm. Both of these peaks are found to be field dependent. Detailed data on emission rate signatures, apparent electron capture cross-sections and defect concentrations are reported for these levels. No Os-related deep level peaks could be clearly delineated in minority-carrier injection DLTS, at this stage, although some evidence is found for a low-energy deep level band.

Field enhanced diffusion of nitrogen and boron in 4H–silicon carbide

A field enhanced diffusion (FED) model is proposed for the observed phenomenon of dopant migration within 4H silicon carbide (4H–SiC) during high temperature annealing. The proposed FED model is based on the combined effects of both dopant diffusion and the in-built p–n junction electric field gradients found within the doped substrate resulting from the presence of the substrate dopants. Measured as-implanted dopant concentration profile data prior to high temperature annealing are utilized as input data for the proposed FED model. The resultant FED profile predictions of the proposed model during annealing are shown to be in excellent agreement with experimental findings. Parameters are extracted using the FED model simulation for the high temperature ionic diffusivity and ionic field mobility for nitrogen dopant in boron co-doped 4H–SiC. The extracted values for the ionic diffusivity and the ionic mobility of the nitrogen donor in boron co-doped 4H–SiC found using the model are 7.2×10−15 cm2 s−1 and 1.6×10−13 cm2 V−1 s−1, respectively.

Two-dimensional p-n junction under equilibrium conditions

For the first time, the idea of a two-dimensional p-n junction formed as a contact between two regions of a quantum-dimensional film with different types of conductivity is proposed. Under equilibrium conditions, the potential distribution and the potential-barrier height were determined. An expression was derived for the width of the surface-charge layer, which depends linearly on the contact potential (external bias) in contrast to the three-dimensional case. The specific capacitance of a two-dimensional p-n junction is virtually independent of the applied potential and depends only on the ambient permittivity. It was shown that, in spite of the fact that the junction electric field is screened only slightly, the Schottky approximation can be used for a description of the properties of such p-n junctions.