Vertical Leakage Research Articles

Role of electron injection on vertical leakage in GaN-on-Si epitaxial layers

The impact of electron injection on vertical leakage current of GaN-on-Si epitaxial layers with an AlN interlayer has been investigated. At high electric field, the AlN interlayer as an energy barrier can suppress the injection of electrons from the silicon substrate into the top buffer layers, and eventually a vertical leakage was reduced by two orders of magnitude at 600 V. At low electric field, the holes flow via dislocations, and prevent the formation of a negative depletion region at the top GaN layer increasing the leakage. The correlation between the vertical leakage and the buffer-related trapping has also been clarified by ramped back-gating characterizations.

420,000 year assessment of fault leakage rates shows geological carbon storage is secure

Carbon capture and storage (CCS) technology is routinely cited as a cost effective tool for climate change mitigation. CCS can directly reduce industrial CO2 emissions and is essential for the retention of CO2 extracted from the atmosphere. To be effective as a climate change mitigation tool, CO2 must be securely retained for 10,000 years (10 ka) with a leakage rate of below 0.01% per year of the total amount of CO2 injected. Migration of CO2 back to the atmosphere via leakage through geological faults is a potential high impact risk to CO2 storage integrity. Here, we calculate for the first time natural leakage rates from a 420 ka paleo-record of CO2 leakage above a naturally occurring, faulted, CO2 reservoir in Arizona, USA. Surface travertine (CaCO3) deposits provide evidence of vertical CO2 leakage linked to known faults. U-Th dating of travertine deposits shows leakage varies along a single fault and that individual seeps have lifespans of up to 200 ka. Whilst the total volumes of CO2 required to form the travertine deposits are high, time-averaged leakage equates to a linear rate of less than 0.01%/yr. Hence, even this natural geological storage site, which would be deemed to be of too high risk to be selected for engineered geologic storage, is adequate to store CO2 for climate mitigation purposes.

Effect of the number of water alternating CO2 injection cycles on CO2 trapping capacity

The CO2 storage capacity is greatly affected by CO2 injection scenario – i.e. water alternating CO2 (WACO2) injection, intermittent injection, and continuous CO2 injection – and WACO2 injection strongly improves the CO2 trapping capacity. However, the impact of the number of WACO2 injection cycles on CO2 trapping capacity is not clearly understood. Thus, we developed a 3D reservoir model to simulate WACO2 injection in deep reservoirs testing different numbers of WACO2 injection cycles (i.e. one, two, and three), and the associated CO2 trapping capacity and CO2 plume migration were predicted. For all different WACO2 injection cycle scenarios, 5000 kton of CO2 and 5000 kton of water were injected at a depth of 2275m and 2125m respectively, during a 10-year injection period. Then, a 100-year CO2 storage period was simulated. Our simulation results clearly showed, after 100 years of storage, that the number of WACO2 cycles affected the vertical CO2 leakage and the capacity of trapped CO2. The results showed that increasing the number of WACO2 cycles decreased the vertical CO2 leakage. Furthermore, a higher number of WACO2 cycles increased residual trapping, and reduced solubility trapping. Thus, the number of WACO2 cycles significantly affected CO2 storage efficiency, and higher numbers of WACO2 cycles improved CO2 storage capacity.

Vertical Current Transport in AlGaN/GaN HEMTs on Silicon: Experimental Investigation and Analytical Model

We investigate the vertical leakage mechanism in metal–organic chemical vapor deposition-grown carbon (C)-doped AlGaN/GaN High Electron Mobility Transistors (HEMTs) on 6-in silicon wafer. Substrate bias polarity-dependent ${I}$ – ${V}_{s}$ , temperature-dependent fitting, and band diagram analysis pointed to the Poole–Frenkel (P–F) type of conduction mechanism for vertical transport in the devices with breakdown as high as 580 V for a buffer of $\textsf {4}~\mu \text{m}$ . Trap activation energy of 0.61 eV was estimated from the P–F fitting which matches well with values reported in the literature. We propose that higher dislocation density leads to shallower traps in the buffer and build an analytical model of dislocation-mediated vertical leakage around this. The variation in leakage as a function of dislocation density at a given field is predicted and is found to be the most abrupt in the range from $\sim 10^{\textsf {7}}$ to $\sim 10^{\textsf {9}}$ cm $^{-\textsf {2}}$ of dislocation density. This can be attributed to a sharp decrease in trap activation energy in the above range of dislocation density, possibly due to complex formation between point defects and dislocations.

Effects of Heterostructure Design on Performance for Low Voltage GaN Power HEMTs

This paper presents a fabless design approach focusing on the impact of heterostructure design on the performance of low voltage GaN power HEMTs. Compared to the standard high voltage design process, low voltage design (<100 V) comes with a unique set of challenges especially concerning breakdown rules. Low voltage simulations reveal less dependence on vertical leakage current and substrate breakdown compared to high voltage designs, and more reliance on buffer leakage and punch-through as the dominant factors leading to breakdown. To analyze the impact of heterostructure design on the device performance, optimization curves are presented for breakdown voltage, on-state resistance, and gate charge. Simulations are performed in Sentaurus TCAD and correlated to known existing experimental results where possible. Trends are presented for the optimization of the channel layer thickness, barrier layer thickness and molar fraction, and impact of an AlN interlayer.

Performance of Recessed Anode AlGaN/GaN Schottky Barrier Diode Passivated With High-Temperature Atomic Layer-Deposited Al2O3 Layer

We have proposed a method of surface passivation with high-temperature atomic layer-deposited (ALD) Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer on the fully recessed anode AlGaN/GaN-based Schottky-barrier diode (SBD) and systematically analyzed the cause of the lateral and the vertical leakage component in the SBD. The forward turn-on voltage of the recessed SBD decreased to 0.38 V from the value of 0.8 V of the nonrecessed SBD due to the lowered barrier height. Application of the ALD Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surface passivation layer to the recessed SBD, which was deposited at higher temperature (550 °C), significantly improved the performances of the proposed SBD such as high on-current of 12 A at 1.5 V and increased breakdown voltage of 780 V with greatly decreased reverse leakage current (at least 3 orders lower in magnitude), compared to the corresponding on-current of 6 A at 1.5 V and breakdown voltage of 510 V of the reference SBD.

Buffer Vertical Leakage Mechanism and Reliability of 200-mm GaN-on-SOI

A comprehensive study on buffer vertical leakage mechanism and buffer reliability of 200-mm GaN-on-SOI is conducted in this paper. The buffer vertical leakage current versus bias is found to sequentially comprise three ranges of low-field leakage, variable-range hopping, and breakdown. The low-field leakage increase at high temperatures has been proven to be dominated by surface leakage. The stressing voltages of buffer time-dependent breakdown (TDB) measurements have a significant impact on shape factor $\beta $ . Stress-induced leakage current is observed in the wear-out phase of the TDB curves. Stress-and-sense measurements in this phase indicate that defects are generated probably around the threading dislocations, where more localized Joule heating and more defects are created by a positive feedback, and finally, the buffer breaks down due to thermal runway. At last, based on the Weibull plot and E-model, the operating voltage is extrapolated to be 470 V corresponding to an expected lifetime of 10 years at 175 °C, with area scaling to the drain terminal of a 150-mm power transistor and failures scaling to 0.01%. The qualification of GaN-on-SOI is crucial for future 200-V GaN power integrated circuit on this platform.

Flow characteristics and dispersion during the vertical anthropogenic venting of supercritical CO2 from an industrial scale pipeline

Pressurized pipelines represent the most reliable and cost effective way of transporting captured CO2 from fossil fuel-fired electricity generation plants for subsequent sequestration. Leakage of CO2 through a small puncture is the most common form pipeline failure during normal operation; such failures could lead to fracture. The study of pipeline depressurization and inventory dispersion behavior is of paramount importance for assessing the possibility of fracture propagation and the impact of CO2 pipeline releases on the surrounding environment. A large-scale fully instrumented pipeline (258 m long, 233mm i.d.) was constructed to study the pressure response, phase transition and dispersion of gaseous, dense and supercritical phase CO2 during vertical leakage through a 15 mm diameter orifice. The fluid pressures and temperatures in the pipeline were recorded to study the pressure response and phase transition inside the pipeline. Video cameras and CO2 concentration sensors were used to monitor the formation of the visible cloud and the gas concentration distribution in the far-field. There was a “two cold, intermediate hot” phenomenon during the vertical release in the dense and supercritical release due to the dry ice particle accumulation near the orifice. The intersection of the jet flow and settling CO2 mixture resulted in complex visible cloud forms in dense CO2 release.

Tidal Response of Groundwater in a Leaky Aquifer—Application to Oklahoma

AbstractQuantitative interpretation of the tidal response of water levels measured in wells has long been made either with a model for perfectly confined aquifers or with a model for purely unconfined aquifers. However, many aquifers may be neither totally confined nor purely unconfined at the frequencies of tidal loading but behave somewhere between the two end‐members. Here we present a more general model for the tidal response of groundwater in aquifers with both horizontal flow and vertical leakage. The model has three independent parameters: the transmissivity (T) and storativity (S) of the aquifer and the specific leakage (K′/b′) of the leaking aquitard, where K′ and b′ are the hydraulic conductivity and the thickness of the aquitard, respectively. If T and S are known independently, this model may be used to estimate aquitard leakage from the phase shift and amplitude ratio of water level in wells obtained from tidal analysis. We apply the model to interpret the tidal response of water level in a US Geological Survey (USGS) deep monitoring well installed in the Arbuckle aquifer in Oklahoma, into which massive amount of wastewater coproduced from hydrocarbon exploration has been injected. The analysis shows that the Arbuckle aquifer is leaking significantly at this site. We suggest that the present method may be effective and economical for monitoring leakage in groundwater systems, which bears on the safety of water resources, the security of underground waste repositories, and the outflow of wastewater during deep injection and hydrocarbon extraction.

The Impact of Ti/Al Contacts on AlGaN/GaN HEMT Vertical Leakage and Breakdown

Enhanced leakage paths below Ti-/Al-based contacts to GaN-on-Si HEMTs have been identified and studied. Through a novel use of the quasi-static capacitance–voltage technique, the depth of these preferential leakage paths was determined to be $\sim 1.6~\mu \text{m}$ , extending down into the superlattice strain relief layer. Along these paths, the material resistivity was reduced by more than a factor of 100 compared to the uncontacted epitaxy. It is suggested that the cause of the additional leakage is decoration of dislocations. This result is important for understanding buffer transport, a critical parameter for breakdown, and buffer charge storage.

Characterization of a carbonate karstic aquifer flow system using multiple radioactive noble gases (3H-3He, 85Kr, 39Ar) and 14C as environmental tracers

Groundwater age in a carbonate karstic aquifer was assessed using a multiple tracer method that enables identification of modern groundwater (recharged after 1955; using 3H-3He, 85Kr CFCs, SF6,), older components (39Ar, 14C) and quantification of the mixing between them. Twelve wells were sampled in the Eastern Mountain Aquifer (EMA) of Israel along two trajectories, from the recharge area in the mountains, to the natural outlets in the Dead Sea area. The concentration of the dissolved 39Ar in the groundwater decreased from 96 to 12% along the trajectories, indicating recent recharge upstream, and groundwater aged more than 800y downstream. Other tracers present a similar general trend of decreasing concentrations with distance from the recharge area at two distinct rates, suggesting two different groundwater flow velocities in the two different groundwater flow paths. In most of the wells, pronounced mixing was observed according to the presence of young (after 1955) and older water components. The fraction of the young water was quantified by tritium (3H) and by the combination of 3H and 85Kr measurements and found to be between 1 and 67%. The wide age distribution is likely caused by the karstic nature of the aquifer with pronounced dispersion and exchange between highly permeable flow channels and stagnant water stored in the rock matrix. Another mixing mechanism is vertical leakage from the upper to the lower sub-aquifer and vice versa according to the groundwater head differences between the two sub-aquifers. Mixing, diffusive exchange and water rock interaction lead to a reduction of 14C in DIC, resulting in an apparent half-life of ∼900 y instead of 5730y for radioactive decay only. This is concluded from the comparison of 14C and 39Ar ages.

On the impact of substrate electron injection on dynamic Ron in GaN-on-Si HEMTs

The impact of electron injection from the substrate on the dynamic Ron of GaN-on-Si High Electron Mobility Transistors (HEMTs) has been investigated by means of back-bias transient and vertical leakage measurements and TCAD simulations. A strong correlation between electrons injected from the substrate and on-state drain current transients is demonstrated. Moreover, the contribution of the electron-type traps in the buffer layer as opposed to the usually studied hole-like traps to the dynamic Ron is discussed. In particular, the impact of electron-like traps for different levels of substrate leakage current is studied. A TCAD model has been developed and calibrated by taking into account both off-state vertical leakage and on-state drain current transient experimental results. The proposed charge dynamic has also been assessed against state-of-the-art theories. This analysis contributes to a deeper understanding of the complex scenario of different types of traps in the buffer layer of GaN-on-Si devices and highlights the impact that trap-states can have on the on-state and off-state currents.

Impact of the substrate and buffer design on the performance of GaN on Si power HEMTs

This paper presents an extensive analysis of the impact of substrate and buffer properties on the performance and breakdown voltage of E-mode power HEMTs. We investigated the impact of buffer thickness, substrate resistivity and substrate miscut angle, by characterizing several wafers by means of DC and pulsed measurement.The results demonstrate that: (i) the resistivity of the silicon substrate strongly impacts on the breakdown voltage and vertical leakage current. In fact, highly resistive substrates may partly deplete under high vertical bias, thus limiting the total potential drop on the epitaxial layers. As a consequence, the vertical IV plots show a “plateau”, that limits the vertical leakage. (ii) the depletion of the substrate may worsen the dynamic performance of the devices, due to an enhancement of buffer trapping. (iii) Larger buffer thickness results in an increased robustness of the vertical stack, due to the thicker insulating region. (iv) the miscut angle (0°, 0.5°, and 1°) can significantly impact on both threshold voltage and the 2DEG density; devices with miscut substrate have higher current density. On the other hand, the dynamic on-resistance variation is comparable in the three cases.

Vertical leakage mechanism in GaN on Si high electron mobility transistor buffer layers

Control of leakage currents in the buffer layers of GaN based transistors on Si substrates is vital for the demonstration of high performance devices. Here, we show that the growth conditions during the metal organic chemical vapour deposition growth of the graded AlGaN strain relief layers (SRLs) can significantly influence the vertical leakage. Using scanning capacitance microscopy, secondary ion mass spectrometry, and transmission electron microscopy, we investigate the origins of leakage paths and show that they result from the preferential incorporation of oxygen impurities on the side wall facets of the inverted hexagonal pyramidal pits which can occur during the growth of the graded AlGaN SRL. We also show that when 2D growth of the AlGaN SRL is maintained a significant increase in the breakdown voltage can be achieved even in much thinner buffer layer structures. These results demonstrate the importance of controlling the morphology of the high electron mobility transistor buffer layer as even at a very low density the leakage paths identified would provide leakage paths in large area devices.

(Invited) Vacancy-Type Defects and Their Carrier Trapping Properties in GaN Studied by Monoenergetic Positron Beams

GaN and its related alloys are the most important semiconductors in the post-scaling-era. The excellent physical properties of GaN make it a promising semiconductor as well for electronic devices used in high-power and high-frequency applications [1]. Recently, techniques to grow GaN on Si substrates (GaN-on-Si) have been intensively studied. Among many requirements that must be met for practical GaN-on-Si devices, reduced vertical leakage current and the ability to block vertical breakdown are the most important. Carbon doping of the GaN layer effectively increases the layer resistance. A high concentration of carbon (> 1019 cm−3) is commonly required to obtain highly resistive GaN layers. This quite high carbon-doping is also expected to introduce point and structural defects in the GaN layer. Positron annihilation is a powerful technique to evaluate vacancy-type defects in semiconductors [2-5]. In the present study, we used monoenergetic positron beams to study the carrier-trapping mechanism of vacancy-type defects in GaN layers grown on Si substrates. Positron annihilation is a non-destructive tool for investigating vacancies in materials. When a positron is implanted into solids, it annihilates with an electron and emits two γ-quanta (Fig. 1). The energy distribution of the γ-rays is broadened by the momentum component of the annihilating electron-positron pair p L. A freely diffusing positron may be localized in a vacancy because of Coulomb repulsion from charged ion cores. Because the momentum distribution of the electrons in the defects differs from that of electrons in the bulk material, these defects can be detected by measuring the Doppler broadening spectra of the annihilation radiation. The change in the Doppler broadened spectra due to the trapping of positrons is shown in Fig. 2 schematically. The resultant changes in the spectra are characterized by the S parameter. Because the electron density in vacancies is lower than that in the bulk, the positron lifetime increases in vacancies. Thus, measurements of positron lifetime spectra are also used to detect vacancy-type defects. Figure 3 respectively show the photoluminescence spectra and the S values for the GaN layers with [C] = 2 × 1016, 9 × 1017, and 1× 1018 cm−3 as a function of the photon energy. The S value started to increase at a photon energy of 2.7 eV and saturated above 3.2 eV. The observed increase in S can be attributed to the change in the defect charge state from positive to neutral due to the trapping of the excited electrons by the defects (V + + e‒ →V 0). The species of positively charged defects was identified as a Ga vacancy (V Ga) coupled with multiple nitrogen (V N) vacancies [V Ga(V N)n]. Figure 4 shows a schematic band diagram of possible transition levels for the vacancy-type defects. The charge transition could occur through the direct capture of electrons emitted from the valence band. Using the onset photon energies which cause the increase/saturation in the S value (1.8, 2.7, and 3.2 eV), the possible transitions are shown as (a), (b), and (c) in Fig. 4. The energy required for the optical transition from CN - to CN 0 and that from CN 0 to CN + is 2.81 eV and 3.18 eV, respectively [5]. Thus, assuming that the electron emitted from CN is captured by vacancy-type defects, the following reaction is possible: CN ( -/0) + V + → CN (0/+) + V 0. The corresponding electron capture processes involving the charge transition of CN are shown as (d), (e), and (f) in Fig. 4. These results suggest that positron annihilation is a useful tool to study the carrier trapping phenomenon by vacancy-type defects in group-III nitride semiconductors. References Krause-Rehberg and H. S. Leipner, Positron Annihilation in Semiconductors, Solid-State Sciences (Springer-Verlag, Berlin, 1999) vol. 127Uedono et al., APEX 8, 051002 (2015). Uedono et al., J. Appl. Phys. 120, 215702 (2016).Uedono et al., Phys. Stat. Sol. B 2017, 1700521. A. Reshchikov et al., Phys. Rev. B 90 (2014) 235203. Figure 1

Two Methods to Detect Poorly Sealed Monitoring Wells Using Pumping Test Data in a Confined Aquifer

A correctly installed monitoring well (MW) has its riser pipe sealed against the borehole wall. When a MW is poorly installed, there is some vertical leakage close to the riser pipe, which creates a hydraulic short circuit (HSC). A static water level is measured in the pipe, but it is not the piezometric level in the aquifer, which is unknown. The piezometric error is the difference between the piezometric level and the static level in the pipe. It yields other errors in determining flow directions, travel times, and well capture areas. The groundwater sampled in the monitored aquifer may be viewed as polluted, whereas it is locally polluted by the faulty MW. This article deals with pumping tests in confined aquifers, for which a poorly sealed MW yields biased drawdown and recovery data. A few solutions to detect an HSC have been proposed, using either a slug test or a pumping test coupled with a tracer test. This article presents two new solutions to detect an HSC: they provide first the piezometric error and then the correct values for drawdown data. The data of a pumping test near Moncton, NB, are used to illustrate the two solutions. They show also that the HSC detection helps to solve previous inconsistencies between different sets of values for transmissivity, T, and storativity, S, as obtained by usual methods for pumping and recovery when short-circuiting is ignored or unsuspected.

Impact of Substrate Resistivity on the Vertical Leakage, Breakdown, and Trapping in GaN-on-Si E-Mode HEMTs

This paper presents an extensive investigation of the impact of the resistivity of the silicon substrate on the vertical leakage and charge trapping in 200 V GaN-on-Si enhancement-mode high-electron mobility transistors. Three wafers having different substrate resistivities were submitted to combined DC characterization, step-stress experiments, and electroluminescence (EL) analysis. The results described within this paper demonstrate that: 1) the use of a highly resistive silicon substrate can increase the vertical breakdown voltage of the transistors, due to the fact that the voltage drop on the GaN buffer is mitigated by the partial depletion of the substrate (this latter causes a plateau region in the drain to substrate I–V characteristic) and 2) highly resistive substrate results in stronger trapping effects, due to the capacitance of the depleted substrate and the resulting backgating effects. The results described within this paper indicate that the choice of the resistivity of the substrate is the result of a tradeoff between high breakdown voltage (that could be in principle achieved through a highly resistive substrate) and the minimization of trapping processes (which can be hardly obtained with a resistive substrate).

Identification of Hydrobiogeochemical Processes Controlling Seasonal Variations in Arsenic Concentrations Within a Riverbank Aquifer at Jianghan Plain, China

AbstractThe arsenic concentration in groundwater varies significantly with time and space in groundwater‐surface water exchange zones. Various processes have been identified that control arsenic concentration distribution and mobility in laboratory systems. However, it is still challenging to identify important processes controlling arsenic concentration distribution at the field scale due to the complex coupling of hydrobiogeochemical processes. In this study, a reactive flow and transport model was used to identify dominant processes controlling arsenic distribution and seasonal variations in groundwater‐surface water exchange zones using Jianghan Plain, China, as an example. The results revealed the importance of river water and groundwater interactions on seasonal changes in arsenic concentration; however, the affected region is limited to within 50‐m distance to the river. The modeling results, unexpectedly, revealed the predominant importance of groundwater extraction to the seasonal variation in arsenic concentration. The groundwater extraction changed the groundwater flow pattern and induced vertical leakage of oxygen‐containing surface water into the aquifer, which triggered a series of biogeochemical reactions that changed groundwater redox conditions and promoted arsenic sorption, resulting in a rapid decrease in arsenic concentrations in groundwater. After groundwater extraction ceased, aquifer recovered to anoxic condition, promoting arsenic release from the sorbed phase, leading to a rapid rebounding in groundwater arsenic concentrations. Overall, this study provided a tool to identify coupled hydrobiogeochemical processes on arsenic spatiotemporal distribution and migration in groundwater.

Fractionation processes of δ13C in a soil-shallow groundwater system of a potential CO2 sequestration site: Wandoan, QLD, Australia

Near-surface leakage detection is often a crucial part of verifying the success of CO2 sequestration projects, and it cannot be achieved without a detailed description of the natural state of an operational site prior to injection. Without baseline studies, it is difficult to define CO2 anomalies outside natural variation in the subsurface that may be related to leakage. CO2 concentrations and δ13C-CO2 values (of DIC, dissolved gas, and soil gas) were investigated to establish a baseline modelling of natural chemical processes leading to CO2 occurrence and δ13C-CO2 fractionation in the soil-groundwater interface on an example at the Glenhaven site in Queensland, Australia. This was analysed within the context of the hydrogeology and hydrogeochemistry of a shallow aquifer system (<20 m depth). The Glenhaven site and its five monitoring station are located in an area which is a candidate for a future small scale carbon storage pilot project. We combine major ion, stable isotope data of groundwater and soil gas as well as physical hydrogeology data with extensive isotope models to explain the pathways and origins of groundwater and CO2. The results indicate shallow aquitard claystone units at the site restrict vertical groundwater leakage and inter-aquifer mixing. Groundwater chemistry is controlled by transpiration of plants, cation exchange, weathering and meteoric recharge to produce Na-Cl and Na-HCO3-Cl type waters. δ18O and δ2H values suggest a shallow meteoric recharge source largely unaffected by evaporation. CO2 concentrations in soil and dissolved in groundwater range between 631 and 47,516 ppm and δ13C values average −17 and −21‰. The mixing of three potential CO2 sources is discussed: 1) the aerobic decay of C3 plant matter, 2) the aerobic decay of C4 plant matter and, 3) shallow coal related CO2. Despite this, the variability of CO2 concentrations and equivocal sources is not likely to hinder leakage detection in the future of site monitoring.

Investigation on Carrier Transport Through AlN Nucleation Layer From Differently Doped Si(111) Substrates

To get a better insight into the vertical leakage mechanism of GaN-on-Si, the carrier transport from n+, n, p+, and p-Si(111) substrates through the AlN nucleation layer was investigated. A plateau in the current-voltage curve was found only for the AlN/p-Si heterojunction due to depletion of the p-Si substrate. Detailed study illustrated that it was the leaky AlN that cannot effectively block the increasing amount of electrons in the inversion layer at the interface and triggered the depletion. Temperature-dependent characterization suggested that the forward vertical leakage mechanism of AlN/Si could be explained sequentially by Ohm’s law, space-charge-limited conduction, variable-range hopping, and trap-assisted tunneling. A model involving shallow donor traps, interface traps, and deep level traps was proposed to explain the leakage characteristics. This paper shows that the carrier concentration of the Si substrates strongly impacts the vertical leakage characteristics, and also that the carrier transport from the Si substrate through the AlN nucleation layer is heavily influenced by traps.