Metallurgical comparison of Au and Au:An:Au contacts on InGaAs,InGaAsP layers

A metallurgical study of the interaction between Au and InGaAs, InGaAsP and the role of the dopant (Zn) in this interaction has been conducted using TEM, AES and x-ray diffraction. Au alloyed with InGaAs reveals a single layer of large and rounded grains (2000Å in diameter). However, alloyed Au:Zn:Au on InGaAs and InGaAsP forms a continuous chain of spikes penetrating into the semiconductor. This spike morphology produces enhanced local current densities across the contact, and may affect laser reliability. A study of the kinetics of the interaction between the Au layer and InGaAs, reveals two major stages. The first stage is dominated by In out-diffusion and Au-rich Au₄In compound formation. In the second stage of the interaction, the Au-rich Au₄In compound starts to dissolve and Au₇In₃, Au₂Ga and Au₃P₂ (in the case of the quaternary layer) are formed. At certain temperatures, the presence of Zn in the Au layer shortens the time required for completing the first stage and beginning the second stage of the interaction. A thermal stability study reveals metallurgical instability at low tempeature (200° C) which does not reach completion even after alloying at 400° C for 4 hr.     

Au and Ag electrical contacts to p-ZnSe

The reverse bias break-down voltage and resistance of Au and Ag contacts sputter deposited on nitrogen doped p-type ZnSe, having free hole concentrations in the low to mid 10¹⁷ cm⁻³ range, have been studied. Samples were heat treated over the range of 150—400°C for times of 15—45 min. The minimum break-down voltage for the Au contacts (3.0 V) was found to occur following heat treatments at 350—400°C for 30 min and for Ag contacts (2.3 V) following heat treatments at 150°C for 45 min. Secondary ion mass spectrometry and Auger electron spectroscopy were used to identify changes in the contacts induced by heat treatments. No evidence was found for the formation of new interfacial compounds, but Au diffused into the ZnSe at T >350°C. The data suggest that conduction through the Au/ZnSe contacts was dominated by avalanche breakdown assisted by deep acceptor levels formed by the diffusion of Au into the ZnSe. The results from the Ag contacts suggest that interfacial O forms a highly doped region in the ZnSe leading to conduction dominated by field emission currents.     

p—GaP与Au／Zn／AuSb的欧姆接触

用 SEM,AES 和 XRD 研究了 Au/Zn/AuSb 多层金属结构与 p-GaP 在525℃合金化4min 后,它们所形成的金属一半导体层的基本特性。当 GaP 的 p 型层空穴浓度是5×1.0~(18)cm~(-3)时,测量出它的比接触电阻是4×10~(-4)Ω·cm~(-2)。它比 AuZn 合金所形成的比接触电阻降低了一个数量级,从而形成了良好的金属-半导体欧姆接触。     

Thermally stable Nb and Nb/Au ohmic contacts to p-GaN

We have investigated Nb single and Nb/Au metallization schemes for the formation of thermally stable ohmic contacts to p-GaN. It is shown that the asdeposited Nb and Nb/Au contacts exhibit rectifying behavior. However, both the contacts produce ohmic characteristics when annealed at 850°C. Measurements show that the 850°C Nb/Au and Nb contacts yield a specific contact resistance of 1.9×10⁻⁸ and 2×10⁻² ωcm², respectively. Schottky barrier heights are found to decrease with increasing annealing temperature. A comparison of the XRD and electrical results shows that the formation of gallide phases such as Ga-Nb and Ga-Au compounds, play a role in forming ohmic contacts. Atomic force microscopy results show that the surface morphology of the Nb contacts is fairly stable up to 850°C, while the Nb/Au contacts are slightly degraded upon annealing at 850°C.     

Au and non-Au based rare earth metal-silicide ohmic contacts to p-InGaAs

The aim of this study is to improve the electrical properties of ohmic contacts that plays crucial role on the performance of optoelectronic devices such as laser diodes (LDs), light emitting diodes (LEDs) and photodetectors (PDs). The conventional (Pd/Ir/Au, Ti/Pt/Au and Pt/Ti/Pt/Au), Au and non-Au based rare earth metal-silicide ohmic contacts (Gd/Si/Ti/Au, Gd/Si/Pt/Au and Gd/Si/Pt) to p-InGaAs were investigated and compared each other. To calculate the specific contact resistivities the Transmission Line Model (TLM) was used. Minimum specific contact resistivity of the conventional contacts was found as 0.111 × 10⁻⁶ Ω cm² for Pt/Ti/Pt/Au contact at 400 °C annealing temperature. For the rare earth metal-silicide ohmic contacts, the non-Au based Gd/Si/Pt has the minimum value of 4.410 × 10⁻⁶ Ω cm² at 300 °C annealing temperature. As a result, non-Au based Gd/Si/Pt contact shows the best ohmic contact behavior at a relatively low annealing temperature among the rare earth metal-silicide ohmic contacts. Although the Au based conventional ohmic contacts are thermally stable and have lower noise in electronic circuits, by using the non-Au based rare earth metal-silicide ohmic contacts may overcome the problems of Au-based ohmic contacts such as higher cost, poorer reliability, weaker thermal stability, and the device degradation due to relatively higher alloying temperatures. To the best of our knowledge, the Au and non-Au based rare earth metal-silicide (GdSi_x) ohmic contacts to p-InGaAs have been proposed for the first time.     

Ohmic contacts on selectively doped AlInAs/GaInAs heterostructures using Ni, AuGe and Au

We studied three different ohmic metals, AuGe-Ni, Ni-AuGe-Au and AuGe-Au, to find the most suitable one for use in selectively doped AlInAs/GaInAs heterostructures. In the past, AuGe-Ni has been the most commonly used metallic structure. However, AuGe-Ni shows a high contact resistance of about 0.2 Ωmm. Using Ni-AuGe-Au, we were able to obtain a low ohmic contact resistance of about 0.1 Ωmm by optimizing the thickness of the Ni layer and the alloying temperature. This resulted, however, in alloyed layers penetrating the semiconductor deeply. More acceptable results were obtained using AuGe-Au, which provided shallow alloyed layers and good surface morphology in addition to a low contact resistance of about 0.1 Ωmm in a wide range of alloying temperatures from 300 to 450°C. Thus we conclude that a simplified structure without Ni is the preferable ohmic metal for selectively doped AlInAs/GaInAs heterostructures.     

Magnetron sputtered vs. thermally evaporated gold contacts in phthalocyanine-based thin film devices

Sandwich-type ITO/phthalocyanine/Au cells, where top gold contact was deposited by either thermal evaporation or magnetron sputtering, have been fabricated. Comparison of electrical characteristics of these cells revealed important distinctions, which are associated with the deposition method.     

AuGe/Au ohmic contacts to n-type InP by hot-plate alloying

The authors report on the fabrication and characteristics of AuGe/Au ohmic contacts to ion-implanted n-type InP. The contacts have smooth surface morphology, excellent adhesion and good contact resistance uniformity. For samples with carrier concentrations of 1.7 * 10/sup 17/ and 1.6 * 10/sup 18/ cm/sup -3/, contact resistances of 0.07 and 0.03 Omega mm, respectively, have been obtained. These values are among the lowest contact resistances reported for n-type InP.<>     

Contact resistance and fretting corrosion of lead-free alloy coated electrical contacts

As lead-free solders replace tin-lead solders in soldering, it is also expected that lead-free solder alloys will be used as contact finish materials for electrical contacts. In this study, the contact resistance and fretting corrosion of tin-silver-copper and tin-copper coatings were investigated and compared with tin-lead eutectic coating. The contact resistance before and after different aging conditions, including mixed flowing gas, steam, and dry heat aging, was examined. Tin-silver-copper and tin-lead alloy coatings have similar performance on contact resistance versus contact normal force after dry heat aging and MFG aging. Severe degradation was found on tin-silver-copper coatings after steam aging. Higher contact force is suggested in the application of tin-silver-copper solder alloy coating than for eutectic tin-lead alloy coatings. Fretting corrosion on tin-silver-copper and tin-copper lead-free alloy coatings was studied and compared with tin-lead coating. Fretting corrosion experiments were conducted and compared at different temperatures and normal forces. In general, tin-silver-copper and tin-copper alloys show equal or better fretting corrosion resistance than tin-lead eutectic alloy at the experimental conditions in this study.     

Au/Ge/Pd ohmic contacts to n-GaAs with the Mo/Ti diffusion barrier

The influences of the As-outdiffusion and Au-indiffusion on the performances of the Au/Ge/Pd/n-GaAs ohmic metallization systems are clarified by investigating three different types of barrier metal structures Au/Ge/Pd/GaAs, Au/Ti/Ge/Pd/ GaAs, and Au/Mo/Ti/Ge/Pd/GaAs. The results indicate that As-outdiffusion leads to higher specific contact resistivity, whereas Au-indiffusion contributes to the turnaround of the contact resistivity at even higher annealing temperature. For Au/Mo/Ti/Ge/Pd/n-GaAs samples, they exhibit the smoothest surface and the lowest specific contact resistivity with the widest available annealing temperature range. Moreover, Auger electron spectroscopy depth profiles show that the existing Ti oxide for the Mo/Ti bilayer can very effectively retard Au-indiffusion, reflecting the onset of the turnaround point at much higher annealing temperature.     

A measurement on electromagnetic noise and change of surface inarcing electric contacts

The authors have observed the relationship between waveform of electromagnetic noise and change of surface for opening Ag-Pd electric contacts. In case of Ag-Pd electrodes, continuous noise is observed in the whole period of arc discharge in both current polarities. Fluctuations of are voltage and noise are large in the middle part of arc discharge duration. The noise decreases in the later half. The authors proposed a classification of noise waveforms and pattern of surface changes. As a result, patterns of noise waveform and changes of electrode surface at various circuit conditions are classified into three categories. In this paper, the authors showed the correlation between pattern of noise waveform and the change of electrode surface     

The role of germanium in evaporated AuGe ohmic contacts to GaAs

Auger depth profiling, electron probe microanalysis, electron beam induced current and conventional scanning electron microscopy have been used to study the inhomogeneous reaction which takes place during the alloying of evaporated AuGe films on (100), n-type GaAs. These measurements have been correlated with I–V and C–V data taken for heat treatment below the AuGe eutectic temperature (360°C) and specific contact resistance measurements above 360°C.The picture which emerges is that of the key role of the germanium in the metallurgical reaction, in addition to its accepted role as the n⁺ dopant. A simple metallurgical model is proposed which is based on the AuGe being the main reactive system at the interface responsible for the formation of the rectangular particles which are the pathways for the current. Minimum contact resistance correlates with the maximum growth of these particles.     

Interdiffusion of the p-InP with Au−Zn,Ti/Au,Pd/Au,Ti/Pd/Au at interface and their electrical properties

 In this report,the interdiffusion between the p-InP with Au-Zn,Ti/Au,Pd/Au and Ti/Pd/Au at interface have been investigated by Auger electron spectroscopy and electron spectroscopy for chemical analysis.The surface morphology for the heat treatment are observed with scanning electron microscopy. It is found that the indiffusion of Au is easier than that of Pd and Ti and the outdiffusion of In is easier than that of P.The combination state of In and Au is formed during the heat treatment of p-InP/Au-Zn. The effects of the alloying temperature and time on the specific contacts resistance of p-InP/Au-Zn system are studided.The low specific contact resistance,p_c=2.4-2.7×10~(-4)Ω-cm~2,is obtained when alloying at 450℃ for 2 min or at 350℃ for 30 min. These results indicate that the specific contact resistance strongly depend on the“interdiffusion degree”.The Zn in Au-Zn ahoy distributes onto the most surface layer of p-InP/Au-Zn system during evaporation process and heat treatment.It may be one of the reasons for the higher specific contacts resistance.     

Effect of deposition temperature on electric conduction and microstructure of Au films

Electric conduction was studied on thin gold films deposited at room (RT = 300 K) and liquid nitrogen temperature (LT = 77 K). Microstructure properties, and surface morphology of metal films were investigated by transmission electron spectroscopy (TEM) and atomic force microscope (AFM). The film thickness was chosen less than several hundred angstroms. Electrical measurement found that the LT film showed several orders lower resistance compared to the film obtained at room temperature at very low (about 100 Å) thickness. TEM study found that the LT films showed much smaller density of grain boundaries than that of the RT samples. In AFM observation, for film thickness of 100 Å, LT film showed smoother and continuous surface while the RT film consisted of discrete islands. When the thickness increased to be 200 Å, the LT film showed much larger-sized grains compared to that of the RT film. It is possible that for LT deposition, two-dimensional larger-sized grains were first formed at low temperature deposition which later extended to be three-dimensional.     

Thermally induced variation in barrier height and ideality factor of Ni/Au contacts to p-GaN

In this paper, we describe the change in barrier heights (ϕ_B) and ideality factors (n) of Ni/Au contacts to p-GaN determined from current-voltage measurements as a result of (a) rapid thermal annealing between 400–700°C under flowing nitrogen, and (b) testing at temperatures of 20–300°C. The lowest barrier height and ideality factor values were obtained from samples annealed at 500–600°C. These results provide supporting evidence that thermal processing helps to remove contaminants at the contact-GaN interface, thus decreasing effective barrier height and consequently, contact resistance.     

Electrical characteristics of thermally stable Ru and Ru/Au ohmic contacts to surface-treated p-type GaN

The electrical and thermal properties of Ru and Ru/Au ohmic contacts on two-step-surface-treated p-GaN have been investigated using current-voltage (I–V) measurements and Auger electron spectroscopy. It is shown that annealing at 700°C for 2 min in a flowing N₂ atmosphere improves the I–V characteristics of the contacts. For example, the annealed Ru and Ru/Au schemes produce a specific contact resistance of 3.4 (±0.9)×10⁻³ and 1.2 (±1.1)×10⁻³ Ωcm², respectively. It is also shown that annealing results in a large reduction (by ∼100 meV) in the Schottky barrier heights of the Ru and Ru/Au contacts, compared to the as-deposited ones. The electrical properties of the two-step-surface-treated Ru/Au contacts are compared with those of the conventionally treated contacts.     

Substrates,contacts and monolithic integration

Substrates and contacts play a critical role in thin-film solar cell device and module performance. They influence light trapping, film growth, impurity levels, doping, stability, yield and laser scribing for monolithic integration. The substrate is also a major cost factor, often accounting for the largest component of the module cost. The interaction between the substrates or contacts with the semiconductor layers can also limit the range of the subsequent semiconductor layer processing parameters. The panel and audience discussed these factors in relation to fabrication, performance and characterization of today's thin-film solar cells and modules. © 1997 John Wiley & Sons, Ltd.     

Annealing temperature effect on electrical and structural properties of Cu/Au Schottky contacts to n-type GaN

Schottky contacts were fabricated on n-type GaN using a Cu/Au metallization scheme, and the electrical and structural properties have been investigated as a function of annealing temperature by current-voltage (I-V), capacitance-voltage (C-V), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) measurements. The extracted Schottky barrier height of the as-deposited contact was found to be 0.69 eV (I-V) and 0.77 eV (C-V), respectively. However, the Schottky barrier height of the Cu/Au contact slightly increases to 0.77 eV (I-V) and 1.18 eV (C-V) when the contact was annealed at 300 °C for 1 min. It is shown that the Schottky barrier height decreases to 0.73 eV (I-V) and 0.99 eV (C-V), 0.56 eV (I-V) and 0.87 eV (C-V) after annealing at 400 °C and 500 °C for 1 min in N₂ atmosphere. Norde method was also used to extract the barrier height of Cu/Au contacts and the values are 0.69 eV for the as-deposited, 0.76 eV at 300 °C, 0.71 eV at 400 °C and 0.56 eV at 500 °C which are in good agreement with those obtained by the I-V method. Based on Auger electron spectroscopy and X-ray diffraction results, the formation of nitride phases at the Cu/Au/n-GaN interface could be the reason for the degradation of Schottky barrier height upon annealing at 500 °C.