Low resistance ohmic contacts to n- and p-InP

The contact properties of various metal combinations, deposited by vacuum evaporation on InP, were studied. Among these metal combinations, Au/Ge + Ni and Au/Zn proved to be most suitable. The former on n-InP (n = 8 × 10¹⁷/cm³) and the latter on p-InP (p = 9 × 10¹⁷/cm³) exhibited specific contact resistances as low as 1.2 × 10^?6 and 1.1 × 10^?4 Ωcm², respectively. The specific contact resistances were analyzed using a four-point method which also accounts for the spreading resistance. Furthermore, the resistances of metal contacts to InP were calculated as a function of doping concentration and were compared with the experimental results. The described contacting technique was successfully applied to the preparation of quaternary lasers.     

The specific contact resistance of Pd2Si contacts on n- and p-Si

The specific contact resistance ρ_c of Al and Pd₂Si contacts has been measured on p- and n-Si substrates of uniform resistivity. The variation of ρ_c with substrate resistivity is described by the following equations:

The specific contact resistance of Al contacts was found to be lower than the values of Pd₂Si contacts on p-Si. Pd₂Si contacts on both n- and p-Si, (111) orientation, become non-ohmic in the resistivity range $\text{0.020?0.10 Ω-}\text{cm}$.The data in this study are not sufficient to distinguish a variation in ρ_c with substrate orientation. Specific contact resistance values of Pd₂Si contacts on $\text{0.005 Ω-}\text{cm}\text{(100) n-}\text{Si}$ and $\text{0.010 Ω-}\text{cm}\text{(100) p-}\text{Si}$ were not significantly different from values expected for the (111) substrates.     

Ohmic contacts in GaAs

Ohmic contacts of n-type GaAs can be reproducibly made to exhibit specific contact resistivities less than 1 × 10^?6 Ω - cm^?2. To do this requires an understanding of the physics involved, a knowledge of the history of previous treatment of the GaAs wafer surface, and processing techniques which are compatible with precisely controlled donor impurity site location determination. The present paper correlates the electrical effects observed in several significant recent developments with theory and interface chemistry to provide workers in the field with a physical understanding of what is essential for reproducible, effective, and reliable ohmic contacts.     

Ohmic contacts to GaAs lasers using ion-beam technology

The ion-beam sputtering technique was used to deposit PtTi contacts to p-type GaAs. With the use of an annealing process, ohmic behavior was eminently enhanced. Specific contact resistance was measured and AES utilized for structural analysis. Specific contact resistance down to 2.4 × 10^-5ω.cm²was achieved. This low specific contact resistance is to our knowledge the lowest reported on p-type GaAs, and is comparable with state-of-the-art PtSi and Cr contacts reported on Si. The contacts also exhibited very stable characteristics. Furthermore, this contacting process, was applied to double heterostructure (DH)-GaAs stripe lasers with excellent results. These results clearly demonstrate the advantage of this process, making it very suitable for industrial applications.     

Temperature coefficient of resistance for p- and n-type silicon

The temperature coefficient of resistance for n- and p-type silicon has been calculated between ?50 and 125°C for a wide range of concentrations and levels of compensation. These results provide a useful guide for the design of silicon integrated resistors.     

Pd/Ge contacts to n-type GaAs

Sintered metal-semiconductor contacts, formed by thin, evaporated layers of Pd and Ge on n-type GaAs, were studied using Auger electron spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, current-voltage measurements, and capacitance-voltage measurements. Prior to sintering, the as-deposited Pd/Ge/GaAs contacts were rectifying and exhibited a reproducible Schottky barrier energy φ_Bn of 0.67±0.02 eV. Auger analysis indicated the initial behavior of the contact structure, upon sintering, to be an interdiffusion and reaction of Pd and Ge on a non-reacting GaAs substrate. Two germanide phases, Pd₂Ge and PdGe, were identified using X-ray diffraction and Auger analysis. The intervening Ge layer prevented the reaction of Pd with the GaAs substrate at low temperatures. Because of the PdGe reaction, φ_Bn increased to approximately 0.85 eV. Sintering at higher temperatures (i.e. between 300 and 400°C) produced additional reactions between Pd and the GaAs substrate. The electrical properties of the contact remained rectifying and φ_Bn exhibited little change from the value of 0.85 eV with the interdiffusion of Pd, Ga, and As. Sintering above 400°C resulted in the formation of ohmic contacts. The diffusion of Ge to the GaAs interface was found to correlate with the onset of ohmic behavior. Current conduction in the contact was best described by thermionic-field emission theory, and a specific contact resistance of 3.5 × 10^?4Ω-cm² was obtained after sintering above 550°C, independent of the initial impurity concentration in the substrate. Over the entire range of sintering temperatures (i.e. at or below 600°C), the interaction between the thin-film layers appeared to be governed by diffusion-controlled, solid-phase processes with no evidence of the formation of a liquid phase. As a result, the surface of the contact structure remained smooth and uniform during sintering.     

Proton bombardment in n- and p-type Ga0.47In0.53As

Ga_0.47In_0.53As epitaxial layers on InP substrate have been subjected to proton bombardment. The resistivity increases up to 10⁴Ω cm for 10¹⁴H⁺/cm² in p-type and 3 · 10¹⁶H⁺/cm² in n-type a_0.47In_0.53As implanted at 77 K. Proton bombardment at 300 K showed this increase in resistivity only for p-type material. Channeling experiments indicated that the damage of the lattice which seems to be responsible for the resistivity increase of n-material can be produced only at low temperature with doses of the order of 10¹⁶H⁺/cm². Crystalline layers implanted with high dose showed blistering effects after heat treatments.     

Ohmic contacts to n-type GaN using Pd/Al metallization

Ohmic contacts to n-type GaN grown by metalorganic chemical vapor deposition were formed using a Pd/Al-based metallization. Ohmic contact resistances and specific contact resistances were investigated as a function of rapid thermal annealing temperature, Pd interlayer thickness, and annealing time. As-deposited Pd/AI was found to produce rectifying contacts while the metallization exhibited ohmic characteristics after annealing at temperatures as low as 400°C. A minimum contact resistance of 0.9 ohm-mm (specific contact resistance = 1.2 × 10⁻⁵ ohm-cm²) was obtained upon annealing at 650°C for 30 s. For comparison, Al and Ti/Al contacts were also investigated. Auger electron spectroscopy, secondary ion mass spectrometry, and x-ray diffraction were used to investigate metallurgical reactions.     

Ohmic contact to p-type GaP

A study was made of the contact properties of a AuBe eutectic and a AuBeNi alloy on p-type GaP. The specific contact resistance varied from 1 × 10^?3 to 7.5 × 10^?5 ω cm² in the acceptor concentration range of 9 × 10¹⁶ to 2 × 10¹⁸ cm^?3. In the sintering temperature range resulting in good ohmic behaviour and low contact resistance the AuBe contacts do not form drops, whereas the AuBeNi contacts became molten; even after melting they wetted the surface of the GaP well. At the temperature of sintering Be diffuses from the contact into the GaP. The diffusion of Be gives rise to an additional acceptor concentration of 5 × 10¹⁸ to 1 × 10¹⁹ cm^?3 beneath the contact surface. Taking this into consideration the concentration-specific contact resistance relationship appears to support a field emission FE conduction mechanism.     

Current-voltage characteristics of GaAs p-i-n and n-i-n diodes

Using the same basic equations as Kazarinov et al.[2], but assuming that the product of the electron drift velocity and of the electron lifetime remains constant, we have derived a new formula for the forward d.c. current—voltage characteristic distinguished by the saturated voltage. We have shown that this formula can describe the measured characteristics of some GaAs p-i-n and n-i-n diodes.     

Gallium-vacancy-dependent diffusion model of ohmic contacts to GaAs

A new model based on gallium-vacancy-dependent diffusion of germanium into gallium arsenide is proposed to explain the ohmic behaviour of an alloyed AuGeNi?n GaAs system. For constructing the model, the following dominating states are assumed to form during alloying; germanium on gallium sites (Ge_Ga^?), germanium on arsenic sites (Ge_As^?), the vacancy complex (Ge_GaV_Ga^?) and neutral pairs (Ge_GaGe_As). This suggests that the formation of donor states (Ge_Ga⁺) is a gallium-vacancy phenomenon and attains a maximum level at an optimum temperature at which acceptor formation rate begins to exceed donor generation. The established theory of grain-boundary diffusion and thermodynamical results are used to compute concentrations of gallium vacancies and donors, respectively. The results indicate that the maximum achievable doping, in practice, is of the order of 5 × 10¹⁸ cm^?3, when an AuGeNi-n GaAs system is alloyed at the optimum temperature. This explains the limitations in obtaining minimum values of contact resistance by alloying techniques.     

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。     

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.     

Exploiting diffusion currents at Ohmic contacts for trap characterization in organic semiconductors

Studying space-charge limited currents enables fundamental insight into the properties of charge carrier transport. However, in unipolar devices with Ohmic contacts, diffusion of charge carriers from the contacts into the intrinsic layer can dominate the current–voltage (J–V  ) characteristics, especially when the devices are thin as in organic electronic devices (∼$\sim$100 nm). Thus, the common approximation of drift-only trap-limited currents (J∼V^l+1$J\sim V^{l+1}$) caused by an exponential distribution of traps is not applicable for determination of the trap distribution. Here, we show by numerical drift–diffusion simulations of unipolar devices with p-doped injection layers (p–i–p devices), how diffusion currents affect the J–V power law depending on the intrinsic layer thickness for typical transport parameters of organic semiconductors. As the thickness dependence of the power law is characteristic of the trap distribution, the distribution can be determined from a simple variation of the device thickness.     

两步合金法制作p-GaN高反电极

利用两步合金法获得了能与p-GaN形成良好欧姆接触的高反射电极.电极的构成采用透明电极 高反射金属方案,厚的Ag层或Al层覆盖在合金后的Ni/Au上以提高电极的反射率,以Pt和Au作为覆盖层,可有效地防止Ag的氧化和团聚,短时间的热处理有助于Ag基电极反射率的提高.可靠性测试表明Ag基电极的稳定性较好,对于Al基电极,热处理后反射镜上出现暗斑,导致其反射率的下降.最终获得了波长在460nm处反射率为74%的Ag基高反射电极.     

Ohmic contacts on high purity P-type silicon

A new method of forming electrical contacts on high purity p-type silicon has been developed. The resultant contacts are ohmic from 18 to 300K. The electrical sparking technique permits localized doping in the contact region of the device while avoiding the over-all high annealing temperatures required by diffusion. Indium solder is used for metallization and attachment of wires to the sparked regions. The process is simple and easily applied to samples for measuring electrical transport properties or to devices, such as silicon solar cells.     

Ohmic contacts on p-type Ga0.47In0.53As/InP

Ohmic contacts of Au and Ag based Zn containing alloys on p-type Ga_0.47In_0.53As have been studied using intermediate layers of Ti and Ni, respectively. Low specific contact resistance in the order of 10⁻⁵ Ωcm² are achieved. In case of AuZn alloy, the Ti intermediate metal layer causes higher contact resistances together with a worse contact morphology in contrast to Ni intermediate layers. However for AgZn contacts Ti adherent layers improve the contact resistances, especially for lower alloying temperatures. Moreover these contacts exhibit significant smoother interfaces as revealed by TEM micrographs. Thus AgZn contacts apply best to low resistive contacting of very thin p-layers forming e.g. the base of a ballistic device.     

Ohmic contacts formed on single- and poly-crystalline silicon using ion implantation and low-temperature annealing

The evolution in integrated-circuit technology is towards lower process temperatures and a consequential decrease in layer junction depths, a step that may not be compatible with ohmic contact formation and low sheet resistance layers using present technology. In this letter, we present a method whereby ohmic contacts are made to antimony ion-implanted layers of both single and polycrystalline silicon that are annealed at temperatures less than 700°C. Experimental results suggest that these contacts and the shallow relatively low sheet resistance layers produced offer considerable promise for future generation integrated-circuit technology.     

Low-resistance Ohmic contacts to digital alloys of n-AlGaN/AlN

Low contact resistance to digital alloys of n-type AlGaN/AlN with high average Al concentration is described. Low-energy electron diffraction was used to evaluate surface precleaning with HCl and buffered HF. The contact metallization consisting of a stack of Ti/Al/Ti/Au, 20/100/45/60 nm in thickness, was e-beam deposited and etch-patterned. The lowest specific contact resistance of 5.6/spl times/10/sup -5/ /spl Omega//spl middot/cm/sup 2/ was obtained after annealing in N/sub 2/ ambient at 700/spl deg/C.     

Impurity distributions and p−n junctions in semiconductors

We have obtained a closed-form solution of the Poisson-Boltzmann equation for a class of quasi-linearly graded p?n junctions. The solution reveals that asymmetric distributions can produce electrostatic potential barriers on the low impurity density side of the junction. For majority carriers these barriers become potential traps producing a secondary space charge next to the primary dipole at the junctions center. The depth of the potential wells depend on the difference in bulk acceptor and donor densities as well as the impurity density slope at the junctions center. Numerical values are given for silicon and germanium.