# Electrical and structural investigation of Pt/n-type GaN Schottky contacts: The possible origin of inhomogeneous barrier

Mohammed Mamor, Marie Pierre Chauvat, Pierre Ruterana

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Mohammed Mamor, Marie Pierre Chauvat, Pierre Ruterana. Electrical and structural investigation of Pt/n-type GaN Schottky contacts: The possible origin of inhomogeneous barrier. Materials Science and Engineering: B, 2024, 310, pp.117756. 10.1016/j.mseb.2024.117756. hal-05051247

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Electrical and structural investigation of Pt/n-type GaN Schottky contacts: The possible

origin of inhomogeneous barrier

Mohammed Mamor<sup>a, *</sup> Marie Pierre Chauvat<sup>b</sup> and Pierre Ruterana<sup>b</sup>

<sup>a</sup>Laboratoire Physique Fondamentale et Appliquée –Safi (LPFA-Safi), Faculté Poly-Disciplinaire, B. P. 4162 Safi, Université Cadi Ayyad, Marrakech, Morocco.

<sup>b</sup> CIMAP, UMR 6252, CNRS, ENSICAEN, Université de Caen-Normandie, CEA, 6 Boulevard du Maréchal Juin, 1400 Caen, France.

ABSTRACT

An ideal metal/GaN interface is not usually possible and the surface states are often present at such
interface and therefore affect the Schottky barrier diode (SBD) performance. In this work the
interface states in Pt/n-type GaN SBD were extracted using temperature dependent forward current-
voltage (I-V-T) characteristics over a large temperature range (80-400 K). The energy profile
distribution of the density of interface states N<sub>SS</sub> (E) and its dependence on the temperature were
determined from the bias and temperature dependence of the measured effective barrier height
Φ<sub>obn</sub>(V, T) and ideality factor n (V, T). It is shown that the interface states density at room
temperature decreases with increasing energy with respect to the conduction band. It is shown that
the effective Schottky barrier height (SBH) and ideality factor are correlated to the density of
interface states. This result suggests that interface states density contributes to barrier
inhomogeneities in Pt/n-type GaN SBD. Fourier transform deep level transient spectroscopy (FT-
DLTS) has been employed to extract qualitative information about the native defects present in as-
grown n-type GaN. From FT-DLTS, two prominent native defects D<sub>2</sub> and D<sub>3</sub> were observed in
GaN. The defect D<sub>2</sub> located at E<sub>C</sub>- 0.56 eV could be associated with impurity at Ga site. The defect
D<sub>3</sub> located at E<sub>C</sub>- 0.26 eV has been assigned to nitrogen-related energy level. These native defects
are interpreted as responsible of the existence of interface states and then to the barrier
inhomogeneities at Pt/n-type GaN contacts. Furthermore, the possible origins of the interface states
at Pt/n-type GaN interface are discussed in terms of the threading dislocations inside the GaN
templates that reach the surface and other possible irregularities at this interface.

**Keywords:** Inhomogeneous barrier height; Thermionic emission model; Surface states density; Deep level transient spectroscopy; Point defects; Transmission electron microscope.

*)Electronic mail: mohammedmamor@yahoo.com
# 1. Introduction

Gallium nitride (GaN) based compounds have generated much interest so far for use in high power, high speed, high temperature and high frequency electronic devices [1-4, 5, 6]. Other examples of GaN-based applications are blue and ultraviolet (UV) light-emitting diodes (LEDs) [7-9]. All these devices require a high quality ohmic and Schottky contacts. Metal (M)/GaN Schottky barrier diode (SBD) have been for many years a subject of intense research because of their role in many GaN based-electronic and optoelectronic devices [10-12]. Furthermore, because of the unique electrical and structural properties of GaN, Schottky diodes based on this semiconductor display excellent performance compared to their Si counterparts [13]. Consequently, a comprehensive understanding of electrical and structural properties associated with GaN Schottky diodes is important for reproducible and reliable fabrication of GaN-based devices. Moreover, accurate preparation of the GaN surface and a precise control of the conditions of the formation of M/GaN contacts are of technological importance for developing GaN based-devices. This, in turn, has led to an increase in interest in the analysis of interface states properties at M/GaN contacts, as interface properties ultimately determine device performance. M/GaN-based electronic and optoelectronic devices are often confronted by the difficulty of controlling the M/GaN interface electrical properties [14, 15, 16, 17, 18]. These properties take account of the interface region; interfacial oxide layer, chemical composition of the interfacial region, the barrier inhomogeneity at M/GaN SBD and most importantly interface defects induced interface states in M/GaN SBD. A most potent origin of interface states at M/GaN contacts is the defects. These defects can be either native defects due to deviation from stoichiometry, such as vacancies and anti-sites related defects or those related to the contact between metal and GaN. These interface states will degrade the quality of the M/GaN structure, resulting in a departure from a pure thermionic-based conduction mode. This departure is often manifested as a high leakage current, an ideality factor value higher than unity and a non- constantly barrier height [19, 20]. Moreover, in the course of metal contact fabrication, an interfacial thin layer might be formed and, hence, separate the metal from the semiconductor, where
carriers (electrons) will tunnel through it. However, the potential drop across this interfacial thin
layer influences the Schottky barrier height (SBH) seen by the electrons. In this case, the interfacial
thin layer and the interface states play a crucial role in the evaluation of the Schottky parameters
such as SBH and ideality factor and, hence, are bias dependent. It has been argued that the barrier
height deduced from the forward current-voltage (I-V) characteristics of SBD is mainly controlled
by the energy distribution of interface states density within the band gap of semiconductor [21]. To
allow a better understanding of the operation of the diode, it is imperative to study the interface
states and determine their energy profile distribution at the M/GaN interface of the diode as well as
its temperature dependence.

In this work, we report on the electrical properties of Pt/n-type GaN interface using temperature dependent current-voltage (I-V-T) characteristics in forward bias. The analyzed forward I-V-T data allow us to obtain the ideality factor (n) and effective zero-bias Schottky barrier height (Φ₀bn). The two parameters, namely Φ₀bn and n are used to extract the density of interface state (Nₛₛ) of the Pt/n-type GaN structure and its temperature dependence as well as their energy profile distribution Nₛₛ (E) in the bad gap of GaN materials.

The aim of this study is to establish a correlation between Φ₀bn and Nₛₛ on the one hand and
between ideality factor, *n* and Nₛₛ on the other hand. This correlation is established in order to
determine the possible origin of inhomogeneous barrier in Pt/n-type GaN SBD. Furthermore, we
report on the results obtained from Fourier transform deep-level transient spectroscopy (FT-DLTS)
combined with transmission electron microscopy analysis (TEM). In particular, we assess from FT-
DLTS the electrical properties of the native defects introduced in the metal organic chemical vapor
deposition (MOCVD) as-grown GaN material and from TEM the structural properties of the defects
at the Pt/n-type GaN interface which could be induced during the Pt metal deposition. An attempt
has been made to show that both native and/or structural defects are considered to be responsible for
the existence of interface states at Pt/n-type GaN interface and consequently for the occurrence of
barrier height inhomogenities.
## 2. Experimental details

The GaN samples used for this investigation with a thickness of 1200 nm were epitaxially grown on (0001) Al₂O₃ c-plane substrate using the MOCVD growth technique. The uniform carrier concentration as determined from capacitance-voltage measurements was evaluated to be about 2×10¹⁷ cm⁻³. The details on the characteristics of the epitaxial layer prior ohmic and Schottky contact fabrication, as well as the diode structure were recently reported [22]. Ohmic contacts of composition Ti/Al/Ni/Au and thicknesses of 15/220/40/50 nm were fabricated on the front side of chemically cleaned n-type GaN followed by annealing under an argon atmosphere at 500 °C for 5 min. Pt/n-type GaN SBD was prepared by evaporating Pt layer, 0.66 mm in diameter and 120 nm thick, in an electron beam deposition system through a mechanical mask. The forward I-V-T data were collected over the temperature range 80-400 K, using a Keithley 2400 source Ammeter and a Janis closed cycle refrigeration system equipped with a DT-470 diode sensor and a Lakeshore 331 controller for temperature displaying. Thereafter, both FT-DLTS and TEM analysis were performed to investigate the defects introduced in MOCVD as-grown n-type GaN materials. In this FT-DLTS, we carry out measurements from 10 to 420 K and it allows data analysis down to a single exponential transient. The TEM sample was prepared using the focused ion beam (FIB) technique in order to obtain electron transparency.

## 3. Results and discussion

### 3.1. Interface states density

The I-V-T characteristics for Pt/n-type GaN that we analyzed are presented in Fig. 1a and the I-V equation was supposed to be that of thermionic emission (TE) model. The current through the metal-semiconductor SBD at forward bias V is described within the TE model by:

$$I_{\text{TE}}(V) = I_{\text{S}} \left[ \exp\left(\frac{q(V-R_{\text{S}}I)}{nk_{\text{B}}T}\right) - 1 \right] \quad (1)$$

where

$$I_{\text{S}} = A^* ST^2 \exp\left(-\frac{\Phi_{0bn}}{k_{\text{B}}T}\right) \quad (2)$$
Here $A^*$ is the effective Richardson constant, $\Phi_{0bn}$ the barrier height, $n$ the ideality factor, $S$ the area of the diode and $T$ the temperature of the diode. The experimental values of $n$ are deduced at each measuring temperature from the slope of the semi-logarithmic $I-V$ characteristics using the relation:

$$n(V, T) = \frac{q}{k_B T} \left( \frac{dV}{d(\ln I)} \right) \qquad (3)$$

Figure 1b illustrates the temperature dependence of the ideality factor $n(V, T)$ on the forward bias at various temperatures. It is observed that there is a slight variation of $n$ with the bias in the low forward-bias region (where the effect of the series resistance ($R_sI$) is negligible; e.g. the straight-line region of the forward-bias semi-logarithmic $I-V$ characteristics), but there is a large variation of $n$ with bias in high forward-bias region due to the large effect of series resistance. Note that the diode exhibits ideality factor higher than unity in the linear region. The higher values of ideality factor in the linear region usually are ascribed to the presence of interface states at metal/semiconductor contacts [23–25]. The measured values of $\Phi_{0bn}$ from forward bias at zero applied voltage ($V=0$ V) were determined from Eqns (2) at various temperatures. As mentioned above, the ideality factors at different temperature were extracted only from the linear part of the semi-logarithmic $I-V$ characteristics. The temperature dependence of the two parameters, namely $\Phi_{0bn}$ and $n$ in our Pt/n-type GaN, however shows strong temperature dependence [22] which indicates the existence of inhomogeneous barrier at the interface. Such inhomogeneous barrier could be considered as a consequence of the presence of interface states at Pt/n-type GaN interface. Furthermore, interface states energy distribution is extracted from experimental forward $I-V$ data plotted in Fig. 1a. In a real Schottky diode, with the interface states in equilibrium with the GaN semiconductor, the high value of ideality factor is bias and temperature dependent and hence, is linked to the density of interface states $N_{ss}$ by [26, 27]:

$$N_{ss}(V, T) = \frac{1}{q} \left[ \frac{\epsilon_i}{\delta} [n(V, T) - 1] - \frac{\epsilon_{sc}}{W_d} \right] \qquad (4)$$

Where $W_d$ is the width of the depletion layer at zero bias, $\epsilon_{sc}$ and $\epsilon_i$ are the permittivity of the GaN semiconductor and the interfacial layer of thickness $\delta$, respectively.
In the case of n-type semiconductor, the energy of interface states $E_{SS}$ below the minimum of conduction band $E_C$ is determined using the relationship [28]:

$$E_C - E_{SS} = \Phi_e - qV \qquad (5)$$

with the barrier height difference with forward bias is expressed by [29]:

$$\Phi_e(V) - \Phi_{0bn} = q \left(1 - \frac{1}{n(V)}\right) (V - R_S I) \qquad (6)$$

By combining the above Eqns (4) together with 5 and 6, and using the real parameters of the Pt/n-type GaN contacts, we calculate the energy distribution profile of the interface states density in the band gap at each temperature as well as its variation as function of temperature at given bias. Fig. 2(a) and (b) shows respectively the energy distribution profile of $N_{SS}$ at room temperature and its temperature dependence at given forward bias, corresponding to value of energy of interface states of about 0.3 eV with respect to $E_C$. As can be seen in this figure, $N_{SS}$ value increases with decreasing $E_C-E_{SS}$. As mentioned above, the interface states could be among the responsible factors for the barrier inhomogeneities at Pt/n-type GaN interface. In this case, when the $N_{SS}$ is very low the measured effective SBH and ideality factor values should be close to those corresponding to homogeneous Pt/n-GaN interface. Figure 3 illustrates the variation of both $\Phi_{0bn}$ and $n$ as a function of the interface states density, $N_{SS}$ in Pt/n-GaN contacts. However, a linear correlation is clearly evident, indicating that when $N_{SS}$ is decreasing, $\Phi_{0bn}$ increases and $n$ decreases. From the experimental data reported in Fig.3, an intercept at the ordinate axis (corresponding to $N_{SS} \approx 0$) is given by the image force lowered mean barrier height value ($\bar{\Phi}_{0bn} = 1.24$ eV) and by the respective ideality factor ($n_{if} = 1.04$) at homogeneous Pt/n-type GaN contacts. Remarkably, the rate of change of $\Phi_{0bn}$ and $n$ with $N_{SS}$ is nearly the same. Similar results have been also obtained for Pd/n-type GaN [30]. Further, the increase of $N_{SS}$ towards the minimum of the conduction band, $E_C$ is most likely attributed to defects located at and close to the surface of the MOCVD as-grown n-type GaN material. With the aim of shedding more light on the origin of interface states at Pt/n-type GaN contact, we have performed FT-DLTS and TEM characterization of Pt/n-type GaN SBD and the results will be presented in the next sections.
## 3.2. Fourier transform deep-level transient spectroscopy study

FT-DLTS measurements were employed to characterize the native defects in the MOCVD as-grown GaN samples. Figure 4 depicts the FT-DLTS spectrum of the Pt/n-type GaN diode in the range of temperature 10-420 K. It is observed that the MOCVD as-grown GaN sample contained in the investigated temperature range, two prominent native defects, labeled D₂ and D₃, located at 325 K and 148 K respectively. The measurement parameters at which DLTS spectrum was recorded are displayed inside Fig. 4. The DLTS signature (i.e. activation energies *E*<sub>T</sub> and capture cross sections for electrons σ<sub>na</sub>) of the two defects were extracted from the Arrhenius plots in Fig. 5 and are given in Table I. However, the defect concentration of evaluated deep levels D₂ and D₃ is estimated using simulation program and is reported in Fig. 6. It is worth to mention that D₂ has lower concentration than D₃. It is clear from the FT-DLTS signature that D₃ (E<sub>C</sub> - 0.26 eV) and D₂ (E<sub>C</sub> - 0.56eV) have approximately the same DLTS signatures as E₁ and E₂, respectively, detected by Hacke et al in hydride vapor epitaxy as grown n-type GaN [31]. Considering the uncertainties in the Arrhenius plot analysis, the activation energies *E*<sub>T</sub> of D₃ and D₂ are very close to the defects EO2 and EO5, respectively observed by Auret et al in organometallic vapor phase epitaxy (OMVPE) as-grown n-type GaN samples [32] and E₁ and E₂, respectively observed by Götz et al in MOCVD as-grown GaN [33] and by Wang et al in molecular beam epitaxy (MBE) as grown n-type GaN samples [34]. Both the defects E₁ and E₂ detected in MOCVD and MBE as-grown n-type GaN [33, 34] or EO2 and EO5 observed in OMVPE as-grown GaN samples [32] are considered as defects associated to emission of electrons from discrete energy levels. The defect observed at 0.6 eV below the conduction band in OMVPE grown n-type GaN samples have been attributed to the substitution of a metallic (iron) impurity atoms at Ga sites [35, 36]. The defect E₁ detected at E<sub>C</sub>-0.26 eV observed Götz et al have been assigned as defect level associated to carbon and/or hydrogen atoms that could be introduced from the methyl radicals during growth of GaN by MOCVD epitaxy [33, 34, 37]. Recently, the defect energy level (0.25 eV) detected in OMVPE as-grown GaN was ascribed to nitrogen vacancy or/and vacancy-related defect [36, 38, 39]. Since our GaN sample was grown by
MOCVD, it is more likely that the D₃ defect detected on our n-type GaN sample is attributed to carbon or hydrogen-related defect.

### 3.3. Transmission electron microscopy

A general view of the microstructure of the investigated diodes can be deduced from the scanning transmission electron microscope image as shown in Fig. 7a. The Pt contact is clearly seen on the top part of the image, the whole structure exhibits the following layers sequence. On top of the sapphire substrate comes first the low temperature GaN buffer layer, as indicated by the small arrows, this layer contains a lot of defects, some are linear but highly inclined, they are dislocations [40] and stacking faults [41]. Due to the shape of the lamella, some of threading dislocations (TD) appear not to reach that surface, the reason is that they have been cut towards the surface which is the thinnest part; small domains (D) are also present (Fig. 7b), these are either small inversion domains [42] or a complex interaction of basal [43] and prismatic stacking faults [44]. In this area the density of the defects is extremely high; therefore, most of them react and annihilate [45]. During the growth of the template, the density of the extended defects decreases rapidly with the reactions of inclined dislocations that annihilate, and only the threading dislocations which have their line oriented along the grow direction continue to propagate until the growth terminates, thus emerging at the layer surface (Fig. 7b, Fig 7c, mark as TD). The darkest part shown in Fig. 7b is the low temperature buffer (white horizontal arrows), it is highly defective, the typical defects in this part are domains (D), many inclined dislocations that react and thus do not propagate to the surface (TD5, TD7, TD8). Prior the thinning of the TEM lamella by FIB, the surface has been protected by deposition a thin carbon layer ‘dark layer, marked c and arrow and then ion assisted nanocrystalline Pt on the top (Fig. 7c). This allows keeping the integrity of the investigated device against gallium ion damage during the FIB operation of the TEM lamella.

The GaN template on which the Pt has been deposited is 3.2 µm thick and highly homogeneous as can be seen in Fig. 7a. The visible defects in this area are only the threading dislocations; at the surface (Fig. 7c), these defects will tend to get many impurities which create states inside the
band gap of the nitride and thus become highly efficient non-radiative recombination centers [46]. As seen in the images, the TDs originate from the interface with the substrate and propagate until the layer surface, as they cannot be terminated inside the template, except when they accidently meet with other same defects with a Burgers vector of opposite sign. In the area of the figure, the density of these threading dislocations is of 7.8 $10^8$cm⁻² which is high in comparison to the free standing GaN templates where it has been reduced to lower than $10^6$cm⁻² [47]. They most probably have introduced active states at the Pt/GaN interface by gettering many types of point defects into their cores. These results suggest that, the barrier height inhomogeneities could be related to the interface defects and dislocations which contribute to generate the electrical active states measured in FT-DLTS and as well as to the inhomogeneous platinum thickness observed in TEM.

## 4. Summary and conclusion

Electrical properties of Pt Schottky contacts fabricated on MOCVD as grown GaN were investigated using forward *I-V-T* characteristics over a wide temperature range (80–420 K). *I-V-T* investigation indicates that the electrical characteristics of Pt/n-type GaN deviated from the ideal case and demonstrate the occurrence of interface states. From the temperature and bias dependence of the ideality factor, the interface states in equilibrium with n-type GaN were extracted and were found at room temperature to decrease with increasing energy with respect to the conduction band and at fixed energy to be weakly temperature dependent. From FT-DLTS results, two prominent defects were detected; 0.25 eV and 0.56 eV below the conduction band. Indeed, the TEM analysis pointed out the presence of threading dislocations underneath the Pt/n-type GaN Schottky contact. Therefore, the TDs, being at the origin of the electrically active defects measured in FT-DLTS, contribute to the non uniform distribution of surface states in the energy gap of GaN and as a direct consequence to the abnormal *I-V-T* behavior due to barrier inhomogeneities in Pt/n-type GaN Schottky contacts. It is likely that the residual defects and threading dislocations play a key role in determining the overall performance of Pt/n-type GaN SBD and further electrical and structural studies of GaN based Schottky diodes with different metal work functions are needed.
## ACKNOWLEDGMENTS

The TEM samples were prepared using a Focused Ion Beam facility, which was acquired through the EQUIPEX GENESIS ANR-11-EQPX-0020 within the "Investissements d'avenir" national Programme with the contribution of the Region Normandie through the FEDER system.
References

[1] K. Doverspike, A. E. Wickenden, S. C. Binarii, D. K. Gaskill, and J. A. Freitas, *Mater. Res. Soc. Symp. Proc.* **395**, 897 (1996).

https://doi.org/10.1557/PROC-395-897

[2] M.S. Shura, R. Gaska, and A. Bykhovski, *Solid-State Electron.* **43**, 1451 (1999).

https://doi.org/10.1016/S0038-1101(99)00088-X

[3] M. Meneghini, C. DeSanti, I. Abid, M. Buffolo, M. Cioni, R. A. Khadar, L. Nela, N. Zagni, A. Chini, F. Medjdoub, G. Meneghesso, G. Verzellesi, E. Zanoni, and E. Matioli, *J. Appl. Phys.* **130**, 181101 (2011).

https://doi.org/10.1063/5.0061354

[4] R. Sun, J. Lai, W. Chen and B. Zhang, *IEEE Access.* **8**, 15529 (2020).

https://doi.org/10.1109/ACCESS.2020.2967027

[5] N. Wu, Z. Xing, S. Li, L. Luo, F. Zeng and G. Li, *Semicond. Sci. Technol.* **38**, 063002 (2023).

https://doi.org/10.1088/1361-6641/acca9d

[6] H. Umeda, "GaN on Si: Epitaxy and Devices", *Wide Bandgap Semiconductors for Power Electronics: Materials Devices Applications*, (Hoboken, NJ: Wiley Online Library). vol. 2, pp. 555-582, 2021.

https://doi.org/10.1002/9783527824724.ch19

[7] S. Nakamura and G. Fasol, in *The Blue Laser Diode* (Springer, Berlin, 1997).

[8] H. Li, C. -J. Chang, S. -Y. Kuo, H. -C. Wu, H. Huang and T. -C. Lu, *IEEE Journal of Quantum Electronics.* **55**, 1 (2019).

https://doi.org/10.1109/JQE.2018.2883158

[9] Y. -L. Lee and W. -C. Liu, *IEEE Transactions on Electron Devices.* **65**, 3305 (2018).

https://doi.org/10.1109/TED.2018.2849353
[10] N. K. R. Nallabala, S. Godavarthi, V. K. Kummara, M. K. Kesarla, D. Saha, H. S. Akkera, G. K. Guntupalli, S. Kumar, and S. V. P. Vattikuti, *Mater. Sci. Semicond. Process.* **117**, 105190 (2020).

https://doi.org/10.1016/j.mssp.2020.105190.

[11] V. Manjunath, N. K. R. Nallabala, C. Yuvaraj, C. Kukkambakam, V. K. Kummara, S. Kumar, S. Sharma, M. V. Lakshmaiah and V. R. M. Reddy, *Appl. Phys. A.* **127**, 46 (2021).

https://doi.org/10.1007/s00339-020-04173-2.

[12] N. K. R. Nallabala, S. V. P. Vattikuti, V. K. Verma, V. R. Singh, S. Alhammadi, V. K. Kummara, V. Manjunath, M. Dhanalakshm and V. R. M. Reddy, *Mater. Sci. Semicond. Process.* **138**, 106297 (2022).

https://doi.org/10.1016/j.mssp.2021.106297.

[13] H. Kim, *Trans. Electr. Electron. Mater.* **25**, 141 (2024).

https://doi.org/10.1007/s42341-024-00512-9

[14] K. Isobe and M. Akazawa, *Japanese J. Appl Phys.* **59**, 046506 (2020).

https://doi.org/10.35848/1347-4065/ab8024.

[15] H. Kim, H.Y. Lee and B.J. Choi, *Appl. Phys. A.* **127**, 647 (2021).

https://doi.org/10.1007/s00339-021-04799-w.

[16] S. Yang, S. Han and K. Sheng, *Semicond. Sci. Techno.* **136**, 024005 (2021).

https://doi.org/10.1088/1361-6641/abca0d.

[17] S. Kumari, R. Singh, S. Kumar, N. V. L. N. Murty, D. Planson, C. Raynaud, C. Sonneville, H. Morel, L. V. Phung and T. H. Ngo, *Semicond. Sci. Technol.* **39** 065016 (2024).

https://doi.org/10.1088/1361-6641/ad4a65.

[18] J. Ran, Y. Song, X Ji, R. Chen, J. Yang, J. Wang and T. Wei, *Mater. Sci. Semicond. Process.* **177**, 108410 July (2024).

https://doi.org/10.1016/j.mssp.2024.108410.
[19] S. J. Moloi and J. O. Bodunrin, *J. Mater Sci: Mater Electron.* **34**, 1712 (2023).
https://doi.org/10.1007/s10854-023-11090-6.

[20] Ö .F. Bakkaloğlu, K. Ejderha, H. Efeoğlu, A. Karataş, and A. Türüt, *J. Mol. Struct.* **1224**, 129057 (2021).
https://doi.org/10.1007/s12633-021-01132-1.

[21] A. Türüt, B. Bati, A. Kökçe, M. Sağlam and N. Yalçin, *Physica Scripta.* **53**, 118 (1996).
https://doi.org/10.1088/0031-8949/53/1/023.

[22] M. Mamor, K. Bouziane, H. Chakir and P. Ruterana, *Physica B Condens. Matter.* **684**, 415965 (2024).
https://doi.org/10.1016/j.physb.2024.415965.

[23] A. Tataroğlu and Ş. Altındal, *J. Alloys Compd.* **18**, 405 (2009).
https://doi.org/10.1016/j.jallcom.2009.04.119.

[24] Ş. Karataş and A. Türüt, *Physica B Condens. Matter.* **381**, 199 (2006).
https://doi.org/10.1016/j.physb.2006.01.412.

[25] İ. Taşçıoğlu, U. Aydemir, Ş. Altındal, B. Kınacı and K. S. Özçelik, *J. Appl. Phys.* **109**, 054502 (2011).
https://doi.org/10.1063/1.3552599.

[26] E. H. Rhoderick and R. H. Williams, "Metal-Semiconductor Contacts," 2nd ed. Clarendon Press, Oxford, UK: Oxford Science, (1988), p. 38.

[27] H. C. Card and E. H. Rhoderick, *J. Phys. D: Appl. Phys.* **4**, 1589 (1971).
https://doi.org/10.1088/0022-3727/4/10/319.

[28] A. Singh, Solid-State Electron. **28**, 223 (1985).
https://doi.org/10.1016/0038-1101(85)90002-4.

[29] A. Türüt, M. Saglam, H. Efeoğlu, N. Yalcin, M. Yildirim, and B. Abay, *Physica B Condens. Matter.* **205**, 41 (1995).
https://doi.org/10.1016/0921-4526(94)00229-O.
[30] M Mamor, *J. Phys. Cond. Mat.* **21**, 335802 (2009).
https://doi.org/10.1088/0953-8984/21/33/335802.

[31] P. Hacke, T. Detchprohm, K. Hiramatsu, and N. Sawaki, *Appl. Phys. Lett.* **63**, 2676 (1993).
https://doi.org/10.1063/1.110417.

[32] F. D. Auret, S. A. Goodman, F. K. Koschnick, J.-M. Spaeth, B. Beaumont and P. Gibart, *Appl. Phys. Lett.* **74**, 2173 (1999).
https://doi.org/10.1063/1.123791.

[33] W. Götz, N. M. Johnson, H. Amano, and I. Akasaki, *Appl. Phys. Lett.* **65**, 463 (1994).
https://doi.org/10.1063/1.112337.

[34] C. D. Wang, L. S. Yu, S. S. Lau, and E. T. Yu, W. Kim, A. E. Botchkarev and H. Morkoç, *Appl. Phys. Lett.* **72**, 1211 (1998).
https://doi.org/10.1063/1.121016.

[35] M. Horita, T. Narita, T. Kachi, and J. Suda, *Applied Physics Express.* **13**, 071007 (2020).
https://doi.org/10.35848/1882-0786/ab9e7c.

[36] V. P. Markevich, M. P. Halsall, L. Sun, L. F. Crowe, A. R. Peaker, P. Kruszewski, J. Plesiewicz, P. Prystawko, S. Bulka, and R. Jakiela, *Phys. Status Solidi* B **260**, 2200545 (2023).
https://doi.org/10.1002/pssb.202200545.

[37] W. I. Lee, T. C. Huang, J. D. Guo, and M. S. Feng, *Appl. Phys. Lett.* **67**, 1721 (1995).
https://doi.org/10.1063/1.115028.

[38] P. Kruszewski, P. Kaminski, R. Kozlowski, J. Zelazko, R. Czernecki, M. Leszczynski and A. Turos, *Semicond. Sci. Technol.* **36**, 035014 (2021).
https://doi.org/10.1088/1361-6641/abe317.
[39] J. Plesiewicz, P. Kruszewski, V.P. Markevich, P. Prystawko, S. Bulka, M. Hallsal, I. Croweb, L. Sunb, and A.R. Peaker, *Microelectron. Eng.* **274**, 111977 (2023).
https://doi.org/10.1016/j.mee.2023.111977.

[40] V. Potin, P. Ruterana, G. Nouet, R. C. Pond, and H. Morkoç, *Phys. Rev. B.* **61**, 5587 (2000).
https://doi.org/10.1103/PhysRevB.61.5587.

[41] P. Vermaut, P. Ruterana, G. Nouet, A. Salvador, A. Botchkarev, B. Sverdlov, and H. Morkoc, in *Proceedings Microscopy of Semiconducting Materials Conference 1995*, Publisher: The Institute of Physics; Editors: A.G. Cullis, A.E. Staton Bevan, **Vol. 146**, 289(1995).

[42] V. Potin, P. Ruterana and G. Nouet, *J. Appl. Phys.* **82**, 2176 (1997).
https://doi.org/10.1063/1.366094.

[43] V. Potin, P. Ruterana, and G. Nouet, *J. Phys. Cond. Mat.* **12**, 10301(2000).
https://doi.org/10.1088/0953-8984/12/49/332.

[44] P. Ruterana, B. Barbaray, A. Béré, P. Vermaut, A. Hairie, E. Paumier, G. Nouet, A. Salvador, A. Botchkarev, and H. Morkoç, *Phys. Rev. B.* **59**, 15917 (1999).
https://doi.org/10.1103/PhysRevB.59.15917.

[45] M. A. Moram, C. S. Ghedia, D. V. S. Rao, J. S. Barnard, Y. Zhang, M. J. Kappers, and C. J. Humphreys, *J. Appl. Phys.* **106**, 073513 (2009).
https://doi.org/10.1063/1.3225920.

[46] M. Albrecht, J. L. Weyher, B. Lucznik, I. Grzegory, and S. Porowski, *Appl. Phys. Lett.* **92**, 231909 (2008).
https://doi.org/10.1063/1.2928226.

[47] M. Lee, D. Mikulik, M. Yang and S. Park, *Scientific. Rep.* **7**, 8587 (2017).
https://doi.org/10.1038/s41598-017-08905-y.
<table><caption>**Table I.** Summary of electronic properties of the two prominent defects introduced in MOCVD as grown *n*-GaN.</caption><thead><tr><th>Defect label</th><th><i>E</i><sub>C</sub> - <i>E</i><sub>T</sub><br>(eV)</th><th>σ<sub>na</sub><br>(cm<sup>2</sup>)</th><th><i>T</i><sup>a</sup><sub>Peak</sub><br>(K)</th><th>N<sub>T</sub><br>(cm<sup>-3</sup>)</th><th>Similar<br>defects</th></tr></thead><tbody><tr><td>D<sub>2</sub></td><td>0.56 ± 0.02</td><td>(8 ± 2) × 10<sup>-16</sup></td><td>325</td><td>(7 ± 1) × 10<sup>11</sup></td><td><i>E</i><sub>2</sub><sup>b</sup>, EO5<sup>c</sup>, <i>E</i><sub>1</sub><sup>d</sup> <i>E</i><sub>2</sub><sup>e</sup>, <i>E</i><sub>3</sub><sup>f</sup></td></tr><tr><td>D<sub>3</sub></td><td>0.26 ± 0.02</td><td>(3 ± 1) × 10<sup>-16</sup></td><td>150</td><td>(2 ± 1) × 10<sup>11</sup></td><td><i>E</i><sub>1</sub><sup>b</sup>, EO2<sup>c</sup>, <i>E</i><sub>1</sub><sup>f</sup></td></tr></tbody></table>

(a) Peak temperature was measured at U<sub>R</sub> = -3V, U<sub>P</sub> = 1.5 V, t<sub>P</sub> = 10<sup>-4</sup> s and T<sub>W</sub> = 0.02 s.

(b) See Reference [31]

(c) See Reference [32]

(d) See Reference [33]

(e) See Reference [34]

(f) See Reference [36]
FIGURE CAPTIONS

**Fig. 1.** (a) The experimental current voltage characteristics of the Pt/n-type GaN Schottky device at various temperature. The inset indicates the temperature dependent forward current density- voltage characteristics only. (b) The forward bias dependent ideality factor *n* (V, T) for Pt/n-type GaN Schottky device at various temperature.

**Fig. 2.** (a) The interface states energy distribution at the Pt/n-type GaN interface at room temperature. (b) The variation of the interface states density as a function of temperature in Pt/n-type GaN Schottky device.

**Fig.3.** Zero-bias SBH and ideality factor as a function of interface states density for Pt/n-type GaN Schottky device.

**Fig. 4.** FT-DLTS spectrum of MOCVD as-grown GaN sample showing the two most prominent defects D₂ and D₃. FT-DLTS spectrum is recorded with reverse bias U$_{R}$ = -3 V, filling pulse U$_{P}$ = 1.5 V and period width T$_{W}$ = 0.02 s.

**Fig.5.** FT-DLTS Arrhenius plots of defects in MOCVD as-grown epitaxial GaN. Open squares and circles are for the defects D₂ and D₃, respectively.

**Fig. 6.** FT-DLTS spectrum of defect D₂ and D₃. The defect concentration of evaluated deep levels is estimated by the simulation (solid lines).

**Fig. 7.** Scanning transmission electron microscope images showing the cross section of the investigated Pt/n-type GaN Schottky diode: a) An overview of the investigated TEM lamella at an edge of the platinum contact (top left), the threading dislocations (TD) inside the GaN have been marked, they run from the interface with sapphire to the surface. b) A magnified view of the interface area with the sapphire substrate, the darkest part is the low temperature buffer (white horizontal arrows).c) The device toward the surface, at the edge of the platinum contact, the Pt film is polycrystalline and exhibits a columnar structure, a close examination of its surface shows that the columns exhibit various heights.
<figure><img src="image_2.png" /><figcaption>Fig. 1</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>Fig. 2</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Fig.3</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig.4</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 5</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Fig. 6</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Fig. 7</figcaption></figure>
<figure><img src="image_9.png" /></figure>