Ohmic Contact Formation to Doped GaN

1995 ◽  
Vol 395 ◽  
Author(s):  
L. L. Smith ◽  
M. D. Bremser ◽  
E. P. Carlson ◽  
T. W. Weeks ◽  
Y. Huang ◽  
...  
Keyword(s):  
Ohmic Contact ◽  
Electron Beam Evaporation ◽  
Integrated Analysis ◽  
Cross Sectional ◽  
Contact Materials ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
P Type ◽  
Ohmic Contact Formation ◽  
Contact Resistivities

ABSTRACTOhmic contact strategies for n- and p-type GaN have been investigated electrically, chemically, and microstructurally using transmission line measurements, high-resolution EELS and cross-sectional TEM, respectively. The contributions to contact performance from work function differences, carrier concentrations, annealing treatments, and interface metallurgy have been examined. The contact materials of Ti, TiN, Au, and Au/Mg were deposited via electron beam evaporation; Al was deposited via thermal evaporation. As-deposited Al and TiN contacts to highly doped n-GaN were ohmic, with room-temperature specific contact resistivities of 8.6×10−5 Ω cm2 and 2.5×10−5 Ωcm2 respectively. The Ti contacts developed low-resistivity ohmic behavior as a result of annealing; TiN contacts also improved with further heat treatment. For p-GaN, Au became ohmic with annealing, while Au/Mg contacts were ohmic in the as-deposited condition. The performance, structure, and composition of different contact schemes varied widely from system to system. An integrated analysis of the results of this study is presented below and coupled with a discussion of the most appropriate contact systems for both n- and p-type GaN.

Effect of Au distribution in NiO/Au film on the ohmic contact formation to p-type GaN

2005 ◽  
Vol 20 (2) ◽  
pp. 456-463 ◽  
Author(s):  
Jiin-Long Yang ◽  
J.S. Chen ◽  
S.J. Chang
Keyword(s):  
Electron Microscopy ◽  
Ohmic Contact ◽  
Incident Angle ◽  
Specific Contact Resistance ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Transmission Electron ◽  
Specific Contact ◽  
P Type

The distribution of Au and NiO in NiO/Au ohmic contact on p-type GaN was investigated in this work. Au (5 nm) films were deposited on p-GaN substrates by magnetron sputtering. Some of the Au films were preheated in N2 ambient to agglomerate into semi-connected structure (abbreviated by agg-Au); others were not preheated and remained the continuous (abbreviated by cont-Au). A NiO film (5 nm) was deposited on both types of samples, and all samples were subsequently annealed in N2 ambient at the temperatures ranging from 100 to 500 °C. The surface morphology, phases, and cross-sectional microstructure were investigated by scanning electron microscopy, glancing incident angle x-ray diffraction, and transmission electron microscopy. I-V measurement on the contacts indicates that only the 400 °C annealed NiO/cont-Au/p-GaN sample exhibits ohmic behavior and its specific contact resistance (ρc) is 8.93 × 10−3 Ω cm2. After annealing, Au and NiO contact to GaN individually in the NiO/agg-Au/p-GaN system while the Au and NiO layers become tangled in the NiO/cont-Au/p-GaN system. As a result, the highly tangled NiO-Au structure shall be the key to achieve the ohmic behavior for NiO/cont-Au/p-GaN system.

An investigation of a nonspiking Ohmic contact to n-GaAs using the Si/Pd system

1988 ◽  
Vol 3 (5) ◽  
pp. 922-930 ◽  
Author(s):  
L. C. Wang ◽  
B. Zhang ◽  
F. Fang ◽  
E. D. Marshall ◽  
S. S. Lau ◽  
...  
Keyword(s):  
Ohmic Contact ◽  
Rutherford Backscattering Spectrometry ◽  
Tunneling Current ◽  
Solid State Reactions ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Transmission Electron ◽  
Specific Contact ◽  
Diffraction Patterns ◽  
Ohmic Contact Formation

A low-resistance nonspiking Ohmic contact to n-GaAs is formed via solid-state reactions utilizing the Si/Pd/GaAs system. Samples with Si to Pd atomic ratios greater than 0.65 result in specific contact resistivity of the order of 10−6 Ω cm2, whereas samples with atomic ratios less than 0.65 yield higher specific contact resistivities or rectifying contacts. Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, and electron diffraction patterns show that a Pd, Si layer is in contact with GaAs with excess Si on the surface after the Ohmic formation annealing. This observation contrasts with that on a previously studied Ge/Pd/GaAs contact where Ohmic behavior is detected after transport of Ge through PdGe to the interface with GaAs. Comparing the Ge/Pd/GaAs system with the present Si/Pd/GaAs system suggests that a low barrier heterojunction between Ge and GaAs is not the primary reason for Ohmic contact behavior. Low-temperature measurements suggest that Ohmic behavior results from tunneling current transport mechanisms. A regrowth mechanism involving the formation of an n+ GaAs surface layer is proposed to explain the Ohmic contact formation.

Formation of Ni/Pt/Au Ohmic Contacts to p-GaN

1997 ◽  
Vol 482 ◽  
Author(s):  
Ja-Soon Jang ◽  
Hyo-Gun Kim ◽  
Kyung-Hyun Park ◽  
Chang-Sub Um ◽  
Il-Ki Han ◽  
...  
Keyword(s):  
Contact Resistance ◽  
Ohmic Contact ◽  
Ohmic Contacts ◽  
Chemical Vapor ◽  
Electron Beam Evaporation ◽  
Specific Contact Resistance ◽  
Metal Thin Films ◽  
Linear Behavior ◽  
Specific Contact ◽  
P Type

AbstractWe report a new Ni/Pt/Au (20/30/80 nm) metallization scheme to achieve a low ohmic contacts to p-type GaN with a carrier concentration of 9.4 × 1016 cm-3. A Mg-doped GaN layer (0.5 μm) was grown on (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD). All metal thin films were deposited on the p-GaN layer in an electron-beam evaporation system. Samples were annealed by a rapid thermal annealing (RTA) process at a range of temperatures from 300 °C to 850 °C under a flowing Ar atmosphere. A circulartransmission line model (c-TLM) was employed to calculate the specific contact resistance, and current-voltage (I-V) data were measured with HP4155A. The Ni/Pt/Au contacts without the annealing process showed nearly rectifying characteristics. The ohmic contacts were formed on the samples annealed at 500 °C for 30 sec and the I-V data showed a linear behavior. The specific contact resistance was 2.1 × 10-2 Ωcm2. However with increasing the annealing temperature above 600 °C, ohmic contacts were again degraded. Auger electron spectroscopy (AES) depth profiles were used to investigate the interfacial reactions between the trilayer and GaN. AES results suggested that Pt plays a significant role in forming ohmic contact as an acceptor at the interface. Atomic force microscope (AFM) also showed that the samples with good ohmic contact have very smooth surface.

TEM Observations of Ti/AlNi/Au Contacts on p-Type 4H-SiC

2010 ◽  
Vol 645-648 ◽  
pp. 729-732 ◽  
Author(s):  
Bang Hung Tsao ◽  
Jacob W. Lawson ◽  
James D. Scofield ◽  
Javier Francisco Baca
Keyword(s):  
Barrier Height ◽  
Ohmic Contact ◽  
Ohmic Contacts ◽  
Low Energy ◽  
Interfacial Structure ◽  
Cross Sectional ◽  
Composite Configuration ◽  
P Type ◽  
Contact Resistivities ◽  
Anneal Temperature

Improved AlNi-based ohmic contacts to p-type 4H-SiC have been achieved using low energy ion (Al+)implantation, the addition of a thin Ti layer, and a novel two-step implant activation anneal process. AlNi/Au contacts with and without Ti were studied, which resulted in contact resistivities around 1.8x10-4 -cm2 and 2.0x10-3 -cm2 respectively. Even though these values were higher than those of the Ti/AlNi/W system, which was the focus of previous studies, the reduced anneal temperature (650 to 700°C) implies that Ti/AlNi/Au is a promising composite configuration. Cross-sectional TEM and EDX were used to investigate the interfacial structure of the contacts. One possible mechanism for the improved ohmic contact behavior is that the addition of Au and Ti resulted in a reduction barrier height.

Ti/AlNi/W and Ti/Ni2Si/W Ohmic Contacts to P-Type SiC

2006 ◽  
Vol 527-529 ◽  
pp. 903-906 ◽  
Author(s):  
Bang Hung Tsao ◽  
Jacob Lawson ◽  
James D. Scofield
Keyword(s):  
Ohmic Contacts ◽  
High Vacuum ◽  
Surface Region ◽  
Contact Layer ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
Main Observation ◽  
The Stability ◽  
P Type ◽  
Contact Resistivities

AlNi and Ni2Si based ohmic contacts to p-type 4H-SiC have been produced using low energy ion implantation, a Ti contact layer, and sequential anneals. Low resistivities were promoted by degenerately (>1020 cm-3) doping the surface region of 4H-SiC epilayers via Al+ implantation. High acceptor activation and improved surface morphology was achieved by capping the samples with pyrolized photoresist and using a two-step anneal sequence in argon. Ti/AlNi/W and Ti/Ni2Si/W stacks of varying Ti and/or binary layer thickness were compared at varying anneal temperatures. AlNi based samples reliably and repeatedly achieved specific contact resistivities as low as 5.5 x10-5 ohm-cm2 after annealing at temperatures of 700-1000°C. For the Ni2Si samples, resistivities as low 4.5x10-4 ohm-cm2 were reached after annealing between 750 and 1100°C. Similarly, a set of Ti/AlNi/Au samples, with or without Ge as an additional contact layer, were prepared via the same procedures. In this case, specific contact resistivities as low as 5.0 x10-4 ohm-cm2 were achieved after annealing the Ti/AlNi/Au samples between 600 and 700°C for 30 minutes in a dynamic argon atmosphere or under high vacuum. The lowest resistivities were realized using thicker (~ 40 nm) Ti layers. I-V analysis revealed superior linear characteristics for the AlNi system, which also exhibited a more stable microstructure after anneal. SIMS and RBS were used to analyze the stability of the stacks subsequent to thermal treatment. AFM analysis demonstrated the superiority of photoresist capping over alternatives in minimizing surface roughness. Linear ohmic behavior after significantly reduced anneal temperature is the main observation of the present study.

scholarly journals Behavior of W and WSix Contact Metallization on n- and p- Type GaN

1999 ◽  
Vol 4 (S1) ◽  
pp. 684-690
Author(s):  
X. A. Cao ◽  
F. Ren ◽  
J. R. Lothian ◽  
S. J. Pearton ◽  
C. R. Abernathy ◽  
...  
Keyword(s):  
Contact Resistance ◽  
Annealing Temperature ◽  
Specific Contact Resistance ◽  
Ohmic Behavior ◽  
Contact Metallization ◽  
Specific Contact ◽  
Heavily Doped ◽  
Sputter Deposited ◽  
Optimum Annealing Temperature ◽  
P Type

Sputter-deposited W-based contacts on p-GaN (NA∼1018 cm−3) display non-ohmic behavior independent of annealing temperature when measured at 25°C. The transition to ohmic behavior occurs above ∼250°C as more of the acceptors become ionized. The optimum annealing temperature is ∼700°C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700°C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to ∼900°C.

Dependence of the Au/Ni/Si/Ni Contact Properties on the Si-layer Thickness and the Annealing Temperature in p-type GaN Epilayers

2002 ◽  
Vol 17 (5) ◽  
pp. 1019-1023 ◽  
Author(s):  
S.J. Yang ◽  
T.W. Kang ◽  
T.W. Kim ◽  
K.S. Chung
Keyword(s):  
Layer Thickness ◽  
Annealing Temperature ◽  
Electron Beam Evaporation ◽  
Nitrogen Atmosphere ◽  
Specific Contact Resistance ◽  
X Ray Diffraction ◽  
Specific Contact ◽  
Potential Applications ◽  
Increasing Temperature ◽  
P Type

The dependences of the properties of Au/Ni/Si/Ni contacts, deposited on p-GaN epilayers by using electron-beam evaporation, on the Si layer thickness and the annealing temperature were investigated with the goal of producing contacts with low specific resistances. The results of the current–voltage (I–V) curves showed that the lowest specific contact resistance obtained for the Au/Ni/Si/Ni contact with a 1200-Å- thick Si layer on p-type GaN annealed at 700 °C for 1 min in a nitrogen atmosphere was 8.49 × 10-4 Ω cm2. The x-ray diffraction (XRD) measurements on the annealed Au/Ni/Si/Ni/p-GaN/sapphire heterostructure showed that Ni3Si, GaAu, and NiGa layers were formed at the Au/Ni/Si/Ni/p-GaN interfaces. While the intensities corresponding to the Ni3Si layer decreased with increasing annealing temperature above 700 °C, those related to the GaAu and the NiGa layers increased with increasing temperature. These results indicate that the Au/Ni/Si/Ni contacts with 1200-Å-thick Si layers annealed at 700 °C hold promise for potential applications in p-GaN-based optoelectronic devices.

In situ Mg surface treatment of p-type GaN grown by ammonia-molecular-beam epitaxy for efficient Ohmic contact formation

2003 ◽  
Vol 82 (5) ◽  
pp. 736-738 ◽  
Author(s):  
H. Tang ◽  
J. A. Bardwell ◽  
J. B. Webb ◽  
S. Rolfe ◽  
Y. Liu ◽  
...  
Keyword(s):  
Molecular Beam Epitaxy ◽  
Surface Treatment ◽  
Ohmic Contact ◽  
Molecular Beam ◽  
Contact Formation ◽  
P Type ◽  
Ohmic Contact Formation
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