Deep Level Transient Fourier Spectroscopy Research Articles

Electrical characteristics and trap signatures for Schottky barrier diodes on 4H-SiC, GaN-on-GaN, AlGaN/GaN epitaxial substrates

The forward and reverse current transport mechanisms, temperature dependence of Schottky barrier height (SBH) and ideality factor, barrier inhomogeneity analysis, and trap parameters for Schottky barrier diodes (SBDs) fabricated on 4H-SiC, GaN-on-GaN and AlGaN/GaN epitaxial substrates are reported. High SBH is identified for Ni/4H-SiC (1.31 eV) and Ti/4H-SiC (1.18 eV) SBDs with a low leakage current density of <10−8 A cm−2 at −200 V. Thermally stimulated capacitance detects the well-known Z1/2 electron trap at E C—0.65 eV in both 4H-SiC SBDs, while an additional deep-level trap at E C—1.13 eV is found only in Ni/4H-SiC SBDs. The vertical Ni/GaN SBD exhibits a promising SBH of 0.83 eV, and two electron traps at E C—0.18 eV and E C—0.56 eV are identified from deep-level transient Fourier spectroscopy. A peculiar two-diode model behavior is detected at metal/GaN/AlGaN/GaN interface of high-electron mobility transistor (HEMT); the first diode (SBH-1 of 1.15 eV) exists at the standard Metal/GaN Schottky junction, whereas the second diode (SBH-2 of 0.72 eV) forms due to the energy difference between the AlGaN conduction band and the heterojunction Fermi level. The compensational Fe-doping-related buffer traps at E C—0.5 eV and E C—0.6 eV are determined in the AlGaN/GaN HEMT, through the drain current transient spectroscopy experiments.

Deep Level Transient Fourier Spectroscopy Investigation of Electron Traps on AlGaN/GaN-on-Si Power Diodes

Many kinds of defects are present in AlGaN/GaN-on-Si based power electronics devices. Their identification is the first step to understand and improve device performance. Electron traps are investigated in AlGaN/GaN-on-Si power diodes using deep level transient Fourier spectroscopy (DLTFS) at different bias conditions for two Schottky contact’s etching recipes. This study reveals seven different traps corresponding to point defects. Their energy level ET ranged from 0.4 eV to 0.57 eV below the conduction band. Among them, two new traps are reported and are etching-related: D3 (ET = 0.47–0.48 eV; σ ≈ 10−15 cm2) and D7 (ET = 0.57 eV; σ = 4.45 × 10−12 cm2). The possible origin of the other traps are discussed with respect to the GaN literature. They are proposed to be related to carbon and nitrogen vacancies or to carbon, such as CN-CGa. Some others are likely due to crystal surface recombination, native defects or a related complex, or to the nitrogen antisite: NGa.

Deep Level Transient Fourier Spectroscopy (DLTFS) and Isothermal Transient Spectroscopy (ITS) in vertical GaN-on-GaN Schottky barrier diodes

The paper explores the Deep Level Transient Fourier Spectroscopy (DLTFS) capabilities in characterizing electrically active traps in vertical GaN-on-GaN Schottky barrier diodes (SBDs). The capacitance-DLTFS (C-DLTFS) experiments reveal a prominent electron trap T2 at EC – 0.56 eV with a density (NT2) of 8 × 1014 cm−3 and a weak presence of another trap at EC – 0.18 eV (T1) with NT1 = 3.8 × 1013 cm−3 in the SBDs. The C-DLTFS acquired with two emission transients (TE = 20.48 ms and 2.048 s) has resulted in identical trap signatures for T1 and T2. Due to the high NT, the trap T2 at EC - 0.56 eV is identified from the current-DLTFS (I-DLTFS) and thermally stimulated capacitance (TSCAP) measurements. Especially the TSCAP results indicate the carrier freeze-out temperature (T < 75 K) in the GaN material. Furthermore, the carrier emission kinetics of the trap T2 is evaluated by performing isothermal transient spectroscopy at a stabilized temperature. The capture time constant of T2 is estimated from the isothermal transients attained with shorter trap-filling pulse widths (<100 ns).

Comprehensive characterization of vertical GaN-on-GaN Schottky barrier diodes

This paper reports comprehensive characterization of vertical GaN-on-GaN Schottky barrier diodes (SBDs) fabricated on free-standing GaN substrates. The GaN active layer properties are evaluated by atomic force microscopy (AFM), secondary-ion mass spectrometry (SIMS), micro-Raman spectroscopy, cathodoluminescence (CL), and deep-level transient Fourier spectroscopy (DLTFS). The GaN SBDs exhibit near-unity ideality factor (n = 1.1), promising Schottky barrier height (SBH) of ΦB = 0.82 eV, low turn-on voltage ∼0.56 V, leakage current density of JR < 5.5 × 10−6 Acm−2 at −100 V, breakdown voltage VBR < −200 V, and less interface state density (NSS < 5 × 1012 eV−1 cm−2) at the Ni/GaN Schottky contact. The forward and reverse current transport mechanisms of the SBD are identified by fitting analysis of measured J-V. Weak temperature dependence of ΦB and n is detected from I–V-T measurements. Similar traps at EC - 0.18 eV and EC - 0.56 are identified in the various SBDs from DLTFS, signifying that these traps are omnipresent defects in the epilayer.

Electrical characterization and extraction of activation energies of the defect states in the LaAlO3/SrTiO3 heterostructure

In this work, we study the electronic properties of defects in the LaAlO3/SrTiO3 heterostructure, which is known to host a high mobility two-dimensional electron gas (2DEG) at the interface. This 2DEG also shows photoconductance, which could be related to defects that act as deep center trapping and releasing carriers by interaction with light. This phenomenon has raised an interest for the identification of deep energy levels in the LaAlO3/SrTiO3 heterostructure. We have studied the defect state properties using electrical characterization such as capacitance–voltage (C–V), current–voltage (I–V) measurements, and deep-level transient Fourier spectroscopy (DLTFS). From C–V and I–V analyses, a hysteresis was observed indicating an effect of mobile charges in the LaAlO3. Using DLTFS, we identify three defect states located at around 0.17 eV below conduction band and at 0.23 and 0.26 eV above the valence band. These defect states were attributed to defects in SrTiO3 such as strontium vacancies or titanium vacancies. We identify a fourth defect state having an energy of about 0.69 eV below the conduction band that could be related to oxygen vacancies in LaAlO3 or in SrTiO3. In addition, the observation of an effect of the electric field with DLTFS indicated that oxygen vacancies might be involved in Fowler–Nordheim or trap-assisted tunneling through the LaAlO3 layer.

Capacitance and Current Deep-Level Transient Fourier Spectroscopy (DLTFS) for the Characterization of Defect States in Mg-Doped GaN-on-Si p+n Diodes

GaN is a promising semiconductor for high power and high frequency devices such as pn diodes [1] and high electron mobility transistors (HEMTs). Moreover, GaN grown on silicon substrates allow the study of new technologies [2]. However, many defects can degrade the performance of the GaN based devices and occur in the form of native point defects, impurities and extended defects. Few defect states were found, such as nitrogen vacancies, Mg dopants or C impurities but they are not well explained. Therefore, in this work we investigated the defect characteristics of Mg-doped GaN-on-Si p+n diodes using the Deep-Level Transient Fourier Spectroscopy (DLTFS). This technique is based on the measurement of capacitance (C-DLTFS) or current (I-DLTFS) transients during charge release from filled traps. It is an electrical characterization technique used to determine and calculate the density N T, the energy position and the capture cross-section σ T of defect states.The p+n diodes were grown by MOCVD on Si substrates. The p+n structure was composed of a 400 nm thick Mg-doped p +-GaN layer at 6x1019 cm-3 and of a 750 nm thick Si-doped n-GaN layer at 3x1016 cm-3. The DLTFS measurements have been performed between 100 K and 425 K with a dynamic signal of frequency of 1 MHz for various reverse voltages U R and pulse voltages U P = -0.5 V for C-DLTFS and U P = 3 V for I-DLTFS. Capacitance-voltage measurements (not shown) evidenced a graded and non-linear p + n junction.The C-DLTFS spectrum (fig 1.a) shows two positive peaks (T1 and T2) respectively at 130 K and at 330 K and the I-DLTFS spectrum (fig 1.b) shows a positive peak at 390 K. For the peaks at high temperature on C-DLTFS and I-DLTFS spectra, average E A values of about 0.83 eV and 0.81 eV were extracted for both spectra respectively (fig 1.c). So, these two peaks are related to the same defect state. Besides, shifts to high temperature values (opposite as for the Poole-Frenkel effect) were observed on both spectra and this could indicate interface traps. Also, when increasing U P to positive values (not shown), the T1 amplitude increases while the T2 amplitude decreases [3]. This defect state might be associated with hole traps at the interface of the p+n junction on the p+ -side of the junction and are tentatively assigned to CN states [4]. For the peak at low temperature (T1), no temperature shift with U R was observed indicating bulk traps in the n-region and an activation energy (E A) of about 0.23 eV was extracted (fig 1.c). This defect is commonly assigned to dislocations related to VN defects or to VN-VG complexes. Moreover, Mg dopants (p-type) for this doping level have an E A value of about 0.25 eV very close to the T1 E A value. So, the graded and non-linear p + n junction could be explained by the Mg dopants diffusion into the n-type region along dislocations, as previously observed [5].[1] Y. Zhang et al., “High-Performance 500 V Quasi- and Fully-Vertical GaN-on-Si pn Diodes,” IEEE Electron Device Lett., vol. 38, no. 2, pp. 248–251, Feb. 2017.[2] M. Ishida et al., “GaN on Si Technologies for Power Switching Devices,” IEEE Trans. Electron Devices, vol. 60, no. 10, pp. 3053–3059, Oct. 2013.[3] Y. Lechaux et al., “Characterization of defect states in Mg-doped GaN-on-Si pn diodes using deep-level transient Fourier spectroscopy,” Semicond. Sci. Technol., vol. 36, no. 2, p. 024002, Dec. 2020.[4] T. Narita et al., “The origin of carbon-related carrier compensation in p-type GaN layers grown by MOVPE,” J. Appl. Phys., vol. 124, no. 21, p. 215701, Dec. 2018.[5] S. Usami et al., “Direct evidence of Mg diffusion through threading mixed dislocations in GaN p–n diodes and its effect on reverse leakage current,” Appl. Phys. Lett., vol. 114, no. 23, p. 232105, Jun. 2019. Figure 1

Suppression and characterization of interface states at low-pressure-chemical-vapor-deposited SiNx/III-nitride heterostructures

Silicon nitride (SiNx) grown by low-pressure chemical vapor deposition (LPCVD) at a reduced growth temperature (650 °C), is utilized for fabrication of GaN metal–insulator-semiconductor (MIS) power devices. An atomically sharp interface between the LPCVD-SiNx and GaN was achieved, featuring a disordered region with only a thickness of 2.5 ~ 5 Å. A fabricated LPCVD-SiNx/GaN/AlGaN/GaN MIS diode exhibits a sharp two-step capacitance–voltage behavior with small frequency dispersion of 0.4 V in the right step. The improved interface was quantified by a well-elaborated constant-capacitance deep-level transient Fourier spectroscopy (CC-DLTFS), delivering quite low density of 1.5×1013cm-2 eV-1 at the level depth of 30 meV and about 4×1011~1.2×1012cm-2eV-1 at the level depth of 1 eV. Distributions of interface states can be described by a proposed physics-based decoupling function featuring an exponential law. A discrete level at the SiNx/GaN border or in the barrier layer with the level depth and the capture cross section being 0.8 eV and 5.5×10-14cm2 respectively, can thus be detached from the interface states.

Characterization of defect states in Mg-doped GaN-on-Si p+n diodes using deep-level transient Fourier spectroscopy

Mg-doped GaN-on-Si p+n diodes have been fabricated and characterized by static electrical and deep-level transient Fourier spectroscopy (DLTFS) measurements. From static capacitance-voltage (C–V) and current–voltage (I–V) characteristics, we estimated the diffusion barrier of the p+n diode close to the GaN band gap at room temperature. The temperature dependence of the capacitance showed freeze-out effect of the Mg-dopants at 200 K. From DLTFS measurements for various reverse bias and pulse voltages, two peaks were found and are composed of different defect states. The first peak with two components was related to diffusion of Mg p-type dopants in the n-GaN and VN-related defects. The two components have activation energies close to 0.25 eV, from valence band and conduction band with a capture cross-section of ∼10−16 cm2. The second peak with two components showed temperature shifts with the pulse height indicating a band-like behavior. This peak was commonly attributed to deep acceptor CN-related defects with an activation energy of E V +0.88 eV and a capture cross-section of 10−13 cm2. A second acceptor level was found, with an activation energy of 0.70 eV and a capture cross-section of 10−15 cm2. This second component was previously attributed to native point defects in GaN.

Reliability improvement of electrically active defect investigations by analytical and experimental deep level transient: Fourier spectroscopy investigations

Abstract This article discusses the importance of analytical and experimental approaches in Deep level transient Fourier spectroscopy in terms of reliability, to support the current research and the utilization of this technique for complex investigations. An alternative evaluation approach is proposed and validated by relevant experiments. Attention is focused on a GaAs p-i-n structure, the undoped layer induced defect conduction type statement difficulty, accurate evaluation of a dual type majority-minority carrier defect complex and possible limitations of the DLTS experimental technique. Comprehensive evaluation is carried out and the method is discussed in detail. In comparison with reference data, higher precision of calculated activation energies, differences even lower as 10−3 order of magnitude, were achieved.

Insight into the Near-Conduction Band States at the Crystallized Interface between GaN and SiN x Grown by Low-Pressure Chemical Vapor Deposition.

Constant-capacitance deep-level transient Fourier spectroscopy is utilized to characterize the interface between a GaN epitaxial layer and a SiN x passivation layer grown by low-pressure chemical vapor deposition (LPCVD). A near-conduction band (NCB) state ELP ( EC - ET = 60 meV) featuring a very small capture cross section of 1.5 × 10-20 cm-2 was detected at 70 K at the LPCVD-SiN x/GaN interface. A partially crystallized Si2N2O thin layer was detected at the interface by high-resolution transmission electron microscopy. Based on first-principles calculations of crystallized Si2N2O/GaN slabs, it was confirmed that the NCB state ELP mainly originates from the strong interactions between the dangling bonds of gallium and its vicinal atoms near the interface. The partially crystallized Si2N2O interfacial layer might also give rise to the very small capture cross section of the ELP owing to the smaller lattice mismatch between the Si2N2O and GaN epitaxial layer and a larger mean free path of the electron in the crystallized portion compared with an amorphous interfacial layer.

DLTS study of InGaAs and GaAsN structures with different indium and nitrogen compositions

In this article Deep Level Transient Fourier Spectroscopy experiments and various evaluation procedures were used to study emission and capture processes of deep energy levels in intentionally undoped InGaAs and GaAsN semiconductor structures. The examined samples, grown by Atmospheric Pressure Metal Organic Vapour Phase Epitaxy on GaAs substrates, were analyzed at various indium and nitrogen concentrations. Main attention was focused on differences in defect distributions, relations in possible composition and growth condition sensitive defect states. Valuable characteristics of particular In/N contents capable to eliminate or reduce specific impurities are discussed. A possible indium dependent dual state InGaAs complex and a nitrogen and growth condition dependent dual type GaAsN complex was introduced/confirmed. The most balanced samples for further utilizations were achieved for In = 8.9% and N = 1%.

Composition Related Electrical Active Defect States of InGaAs and GaAsN

This paper discusses results of electrically active defect states - deep energy level analysis in InGaAs and GaAsN undoped semiconductor structures grown for solar cell applications. Main attention is focused on composition and growth condition dependent impurities and the investigation of their possible origins. For this purpose a widely utilized spectroscopy method, Deep Level Transient Fourier Spectroscopy, was utilized. The most significant responses of each sample labelled as InG2, InG3 and NG1, NG2 were discussed in detail and confirmed by simulations and literature data. The presence of a possible dual conduction type and dual state defect complex, dependent on the In/N composition, is reported. Beneficial characteristics of specific indium and nitrogen concentrations capable of eliminating or reducing certain point defects and dislocations are stated.

Electrophysical Properties of GaAs P–I–N Structures for Concentrator Solar Cell Applications

Abstract This paper is dedicated to electro-physical characterisation of a GaAs p-i-n structure grown for solar cell applications, which was carried out by light and dark current-voltage (I–V) and Deep Level Transient Fourier Spectroscopy (DLTFS) methods. The conversion efficiency and open-circuit voltage were determined from I–V measurement at 1 and 20× sun light concentrations. Three electron like defects TAn1, TAn2, TDn and one hole like defect TBp obtained by DLTFS measurements were confirmed. The origin of these defect states was stated as native GaAs impurities.

Defect characterization of proton irradiated GaAs pn-junction diodes with layers of InAs quantum dots

In order to expand the technology of III-V semiconductor devices with quantum structures to both terrestrial and space use, radiation induced defects as well as native defects generated in the quantum structures should be clarified. Electrically active defects in GaAs p+n diodes with embedded ten layers of InAs quantum dots (QDs) are investigated using Deep Level Transient Fourier Spectroscopy. Both majority carrier (electron) and minority carrier (hole) traps are characterized. In the devices of this study, GaP layers are embedded in between the QD layers to offset the compressive stress introduced during growth of InAs QDs. Devices are irradiated with high energy protons for three different fluences at room temperature in order to characterize radiation induced defects. Seven majority electron traps and one minority hole trap are found after proton irradiation. It is shown that four electron traps induced by proton irradiation increase in proportion to the fluence, whereas the EL2 trap, which appears before irradiation, is not affected by irradiation. These defects correspond to electron traps previously identified in GaAs. In addition, a 0.53 eV electron trap and a 0.14 eV hole trap are found in the QD layers before proton irradiation. It is shown that these native traps are also unaffected by irradiation. The nature of the 0.14 eV hole trap is thought to be Ga-vacancies in the GaP strain balancing layers.

Defect distribution in InGaAsN/GaAs multilayer solar cells

Deep Level Transient Fourier Spectroscopy (DLTFS) experiments were realized to study emission and capture processes in InGaAsN multilayer solar cells grown on GaAs substrates by Atmospheric Pressure Metal Organic Vapor Phase Epitaxy (APMOVPE). As a referent structure for comparison purposes a basic GaAs p–n sample grown in the same system was also utilized. All the structures exhibited variety of deep energy levels with high concentrations. In addition to the most commonly described arsenic antisite defect, with activation energies 0.73–0.78eV, possible traces of oxygen–arsenic vacancies with 0.52eV and nitrogen interstitial complexes were evaluated. Most dominant electron trap at about 0.53eV below the conduction band EC was observed at different measurement conditions. Based on various references, this electron trap can be associated with a split interstitial defect containing two nitrogen atoms on the same As lattice site. Calculated energies and possible origins of these results were confirmed by Arrhenius curve comparison.

DLTFS Investigation of Ingaasn/Gaas Tandem Solar Cell

Abstract In this paper authors present the results of identification of emission and capture processes in tandem solar cell structures based on quaternary InGaAsN semiconductor alloys by DLTFS (Deep Level Transient Fourier Spectroscopy) and by ana- lytical evaluation processes. The energies of five trap levels ET1=0.77 eV, ET2=0.47 eV, ET3=0.64 eV, HT1=0.62 eV and HT2=0.53 eV were identified with reliable accuracy. These values were obtained by available analytical procedures, verified by simulations and confirmed by reference structures with basic layer types and compared with possible reference trap data. Native structural defects in GaAs were stated as the origin of these deep energy levels

Capacitance properties and simulation of the AlGaN/GaN Schottky heterostructure

Abstract The paper presents the results of capacitance measurements on GaN/AlGaN/GaN Schottky heterostructures grown on an Al 2 O 3 substrate by Low-Pressure Metal–Organic Vapour-Phase Epitaxy (LP-MOVPE). Dependences of the capacitance–voltage (CV) characteristics on the frequency of the measuring signal allow analysing the properties of the 2D electron gas (2DEG) at the AlGaN/GaN heterojunction. Exact location of the hetero-interface below the surface (20 nm) was determined from the concentration profile. Temperature variations of the CV curves reveal the influence of bulk defects in GaN and of the traps at the AlGaN/GaN interface. Electrical activity of these defects was characterized by capacitance Deep Level Transient Fourier Spectroscopy (DLTFS). Experimental results of CV measurements were supported by simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure in dependence on the influence of the concentration of donor-like traps in GaN and of the temperature upon the CV curves.

Luminescence properties of hole traps in homojunction gallium nitride diodes grown by metal organic vapour phase epitaxy

A detailed investigation on p–n junction diodes of GaN using deep level transient Fourier spectroscopy (DLTFS) has been carried out. The typical deep level spectra on the various diodes on the same wafer demonstrate three electron levels labelled as E1, E2 and E3 and a hole trap H1 together with a broad band constituting three new hole levels H2, H3 and H4 therein. The electrical parameters like activation energy, trap concentration and capture cross section due to the observed levels have been measured for the comparison with the literature. The hole levels H1–H4 are found to be potentially involved in the radiative recombination and thereby, the luminescence role of the levels in the device is discussed.

Deep levels in GaInAs grown by molecular beam epitaxy and their concentration reduction with annealing treatment

X-ray diffraction (XRD), current–voltage ( IV), capacitance–voltage ( CV), deep-level transient Fourier spectroscopy (DLTFS) and isothermal transient spectroscopy (ITS) techniques are used to investigate the thermal annealing behaviour of three deep levels in Ga 0.986In 0.014As heavily doped with Si (6.8 × 10 17 cm −3) grown by molecular beam epitaxy (MBE). The thermal annealing was performed at 625 °C, 650 °C, 675 °C, 700 °C and 750 °C for 5 min. XRD study shows good structural quality of the samples and yields an In composition of 1.4%. Two main electron traps are detected by DLTFS and ITS around 280 K, with activation energies of 0.58 eV and 0.57 eV, capture cross sections of 9 × 10 −15 cm 2 and 8.6 × 10 −14 cm 2 and densities of 2.8 × 10 16 cm −3 and 9.6 × 10 15 cm −3, respectively. They appear overlapped and as a single peak, which divides into two smaller peaks after annealing at 625 °C for 5 min. Annealing at higher temperatures further reduces the trap concentrations. A secondary electron trap is found at 150 K with an activation energy of 0.274 eV, a capture cross section of 8.64 × 10 −15 cm 2 and a density of 1.38 × 10 15 cm −3. The concentration of this trap level is also decreased by thermal annealing.

Deep levels in GaInNAs grown by molecular beam epitaxy and their concentration reduction with annealing treatment

Deep-level transient Fourier spectroscopy (DLTFS) technique is used to investigate the thermal-annealing behaviour of at least five deep levels in two samples of Ga 0.987In 0.013N 0.0043As 0.9957, one medium doped with Si (2 × 10 16 cm −3) and the second one heavily doped with Si (1 × 10 18 cm −3) grown by molecular beam epitaxy (MBE). The thermal-annealing study was done at 650, 700, 750 and 800 °C for 5 min. One main electron trap with activation energy of 0.97 eV, a capture cross section of 5.5 × 10 −11 cm 2 and a density of 3.2 × 10 14 cm −3 is detected for the medium-doped as-grown sample. For the heavily doped sample one main electron trap with activation energy of 0.35 eV, a capture cross section of 7.1 × 10 −14 cm 2 and a density of 2.2 × 10 15 cm −3 is detected. For the heavily doped sample, this electron trap only decreases its density as the annealing temperature increases. No more deep centres appear with annealing. For the medium-doped sample, the main electron trap decreases its density as the annealing temperature increases, but unlike the heavily doped sample, four more deep centres appear, depending on the annealing temperature. Their annealing temperature dependence and possible origin of the electron traps are reported for the first time.