Abrupt GaN/p-GaN:Mg junctions grown via metalorganic chemical vapor deposition (original) (raw)
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Japanese Journal of Applied Physics, 2003
Mg redistribution into a subsequently regrown GaN epilayer by metalorganic chemical vapor deposition (MOCVD) is studied. Dopant profiles from secondary ion mass spectrometry (SIMS) on n-p-n GaN samples have been analyzed. The regrowth study in a Mg-free reactor reveals that a Mg-rich film is present on MOCVD as-grown GaN:Mg base layers and can be removed by an acid etch, and that a slow Mg decay into the sequentially regrown GaN results from this Mg-rich surface film. We believe the commonly seen Mg memory effect in MOCVD causes the accumulation of Mg on the surface. From a MOCVD regrowth on n-p-n GaN grown by molecular beam epitaxy (MBE), the Mg diffusion constant is calculated to be about 3 Â 10 À15 cm 2 /s at 1160 C for Mg concentrations between 5 Â 10 17 cm À3 and 1 Â 10 19 cm À3 . The roles of memory effect, surface segregation, and diffusion associated with Mg are addressed.
Incorporation of Mg in GaN grown by molecular beam epitaxy
Journal of Crystal Growth, 1999
We report Mg doping experiments in GaN grown by plasma-enhanced molecular beam epitaxy on sapphire and GaAs substrates. Secondary ion mass spectrometry was used to measure the Mg concentration as a function of Mg flux. Our data show a linear dependence at low fluxes and then tend to saturate, in agreement with the measurements at higher fluxes by Guha et al. We model this in terms of two interacting layers of Mg atoms on the GaN surface, one chemisorbed, the other physisorbed. We suggest that surface stoichiometry is an essential factor in determining doping efficiency and is responsible for the observed temperature-dependence of Mg incorporation.
Improvements in the Annealing of Mg Ion Implanted GaN and Related Devices
IEEE Transactions on Semiconductor Manufacturing, 2016
The activation of ion implanted p-type dopants in GaN is notoriously difficult as the extremely high temperatures required to activate implanted Mg also damage the GaN crystal. In this paper, we present refinements to our novel annealing process (symmetric multicycle rapid thermal annealing) to reduce surface damage and contamination responsible for elevated leakage currents and non-ideal diode behavior. Furthermore, we apply the technique to Mg-implanted bulk GaN substrates to enable vertical power device structures, demonstrating rectifying p-in junctions. In addition, the technique was applied for edge termination in both p-in and Schottky barrier diodes, realizing floating guard ring and junction termination extension structures. The processes demonstrated here represents a key enabling step for future GaN-based power devices.
Electrical characterization of Mg-doped GaN grown by metalorganic vapor phase epitaxy
Applied Physics Letters, 1996
We have applied frequency-dependent capacitance measurements and admittance spectroscopy on GaN:Mg to study the electronic states associated with Mg doping. Metalorganic vapor phase epitaxy GaN:Mg samples with two different Mg doping levels were grown and thermally annealed in nitrogen. Lateral dot-and-ring Schottky diodes using Au/Ti were fabricated. Frequency-dependent measurements on these diodes show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high-frequency modulation. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of one impurity-related acceptor level in the higher Mg-doped sample with an activation energy of 136 meV. For the lower Mg-doped sample, two acceptor levels at 124 and 160 meV were observed. We believe these levels are most probably associated with the Mg acceptor state itself, possessing energy levels which are very close to the results previously reported in the literature.
Applied Physics Letters, 2008
We demonstrate that relatively small GaN substrate misorientation can strongly change hole carrier concentration in Mg doped GaN layers grown by metalorganic vapor phase epitaxy. In this work intentionally misoriented GaN substrates ͑up to 2°with respect to ideal ͗0001͘ plane͒ were employed. An increase in the hole carrier concentration to the level above 10 18 cm −3 and a decrease in GaN:Mg resistivity below 1 ⍀ cm were achieved. Using secondary ion mass spectroscopy we found that Mg incorporation does not change with varying misorientation angle. This finding suggests that the compensation rate, i.e., a decrease in unintentional donor density, is responsible for the observed increase in the hole concentration. Analysis of the temperature dependence of electrical transport confirms this interpretation.
Journal of Crystal Growth, 2005
An Mg-doped p-GaN layer was grown by the metalorganic chemical vapor deposition method. The dissociation extent of hydrogen-passivated Mg acceptors in the p-GaN layer through Mg activation annealing was estimated by using room-temperature cathodoluminescence (CL) spectroscopy. The CL measurement revealed that the CL spectra intensities tend to increase with increasing the activation annealing temperature. The sample annealed at 925 1C showed the most intense emission and the narrowest width among the emission peaks. Consequently, it was the most excellent dissociation extent of Mg-H complexes caused by the Mg activation annealing. The hole concentration under this optimum condition was 1.3 Â 10 17 cm À3 at room temperature. The photoluminescence (PL) measurement showed a 2.8 eV band having characteristically a broad peak in heavily Mg-doped GaN at room temperature. By analyzing the PL results, we learned that this band was associated with the deep donor-acceptor pair (DAP) emission rather than with the emission caused by the transition from the conduction band to deep acceptor level. The four emission peaks in the resolved 2.8 eV band were emitted by transiting from deep donor levels of 0.14, 0.26, 0.40, and 0.62 eV below the conduction band to the shallow Mg acceptor level of 0.22 eV above the valence band.
Nanoscale Research Letters, 2018
Inefficient Mg-induced p-type doping has been remained a major obstacle in the development of GaN-based electronic devices for solid-state lighting and power applications. This study reports comparative structural analysis of defects in GaN layers on freestanding GaN substrates where Mg incorporation is carried out via two approaches: ion implantation and epitaxial doping. Scanning transmission electron microscopy revealed the existence of pyramidal and line defects only in Mg-implanted sample whereas Mg-doped sample did not show presence of these defects which suggests that nature of defects depends upon incorporation method. From secondary ion mass spectrometry, a direct correspondence is observed between Mg concentrations and location and type of these defects. Our investigations suggest that these pyramidal and line defects are Mg-rich species and their formation may lead to reduced free hole densities which is still a major concern for p-GaN-based material and devices. As freestanding GaN substrates offer a platform for realization of p-n junction-based vertical devices, comparative structural investigation of defects originated due to different Mg incorporation processes in GaN layers on such substrates is likely to give more insight towards understanding Mg self-compensation mechanisms and then optimizing Mg doping and/or implantation process for the advancement of GaN-based device technology.
Effect of growth conditions on electrical properties of Mg-doped p-GaN
Journal of Crystal Growth
In this work the effect of carrier gas and post-growth activation conditions on the electrical properties of Mg-doped p-GaN single layers grown in a vertical flow close-coupled showerhead MOCVD system is investigated. The results of Hall effect measurements show that although the optimal Mg precursor flow rate depends on the growth atmosphere and is smaller when N 2 is used as a carrier gas, similar electrical properties could be realized with both H 2 and N 2 carrier gases. The results of SIMS analysis demonstrate that while Mg incorporation is higher for N 2 carrier gas, the efficiency of Mg activation is higher when H 2 is used as carrier gas. We have also observed that the structural quality of N 2 grown layers is substantially lower compared to the H 2 case. r