Janne-Wha Wu

Excellent Au/Ge/Pd ohmic contacts to n-type GaAs using Mo/Ti as the diffusion barrier

Au/Ge/Pd metallization system using Mo/Ti as the diffusion barrier between the Au overlayer and the Ge/Pd underlayer has been performed for the first time to achieve excellent ohmic contacts to n+-GaAs with the Si-doping concentration of about 2×1018 cm-3. The minimum specific contact resistivity as low as 1.2×10-7 Ωcm2 can be obtained after the rapid thermal annealing at 325°C for 60 s, which is much lower than those of the conventional Au/Ge/Pd metallization systems. Furthermore, the available annealing temperature range for such low specific contact resistivities is also significantly extended from 325°C to 400°C. The improvement is attributed to the effective retardation of As-outdiffusion by the Mo/Ti barrier.

The thermal stability of ohmic contact to n-type InGaAs layer

The thermal stability of ohmic contact to n-type InGaAs layer is investigated. When Ni/Ge/Au is used as the contact metal, the characteristics of the ohmic contact are degraded after thermal treatment. The specific contact resistance of (Ni/Ge/Au)-InGaAs ohmic contact after annealing at 450°C is about 15 times larger than that of as-deposited sample. This is due to the decomposition of InGaAs and the interdiffusion of Ga and Au. A new phase of Au4ln appears after annealing at 300°C. While in the case of Ti/Pt/Au, Au does not penetrate into the InGaAs layer as revealed by secondary ion mass spectroscopy. The specific contact resistance of (Ti/Pt/Au)-InGaAs ohmic contact after annealing at 450°C is eight times larger than that of as-deposited sample. Therefore, the thermal stability of (Ti/Pt/Au)-InGaAs ohmic contact is better than that of (Ni/Ge/Au)InGaAs ohmic contact.

Silicon Delta Doping of GaInP Grown by Low-Pressure Metalorganic Chemical Vapor Deposition

Silicon delta doping in GaInP material has been demonstrated by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) and characterized by Hall-effect and capacitance-voltage (C-V) measurements. The mobility enhancement of delta-doped samples over their corresponding uniformly doped samples was observed. High sheet carrier density of N S=1.21×1013 cm-2 could be obtained. A sharp carrier distribution profile with the full width at half maximum of 25 A has been achieved.

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.

Anomalous mobility enhancement in heavily carbon‐doped GaAs

An anomalous mobility enhancement and metallic‐type conductivity were observed in heavily carbon‐doped GaAs grown by low‐pressure metalorganic chemical vapor deposition. The 77 K mobility was slightly lower than that of 300 K for hole concentration between 1×1018 and 4×1018 cm−3. However, the 77 K mobility was enhanced from p≳4×1018 cm−3, and the 300 K mobility slowly decreased with increasing hole concentration that ranged from 7×1018 to 3×1019 cm−3. As a result, the 77 K mobility was around 50%–60% greater than the 300 K mobility due to the metallic‐type conductivity.

Passivation of GaAs Power Field-Effect Transistor Using Electron Cyclotron Resonance Chemical Vapor Deposition Silicon Nitride Technique

Monolithic microwave integrated circuit (MMIC) chips are typically passivated with dielectric films to improve their long-term environmental reliability. Improper passivation generally degrades chip performance and reduces wafer yield. This paper reports the change of metal-semiconductor field-effect transistor (MESFET) parameters after silicon nitride passivation using electron cyclotron resonance chemical vapor deposition (ECR-CVD). In general, the changes in the electrical parameters after passivation are small. Gate-drain breakdown voltage of the MESFETs after ECR-CVD passivation is significantly improved compared to that after PECVD. The microwave characteristics of the high-powered MESFETs passivated using ECR-CVD silicon nitride are also reported in this paper.

High-performance Au/Ti/Ge/Pd ohmic contacts on n-type In0.5Ga0.5P

High-performance Au/Ti/Ge/Pd ohmic contacts on n+-In0.5Ga0.5P have been fabricated for the first time. Using an n+-In0.5Ga0.5P epitaxial layer grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with a Si dopant concentration of about 2×1018 cm-3, the minimum specific contact resistivity is as low as 1.2×10-5 Ωcm2, which is much lower than that of AuGeNi contacts after rapid thermal annealing at 400°C for 60 s. The thermal stability of the Au/Ti/Ge/Pd system is significantly higher than that of conventional AuGeNi due to the introduction of the Ti barrier layer. Many holes and islands are observed on the surfaces of samples annealed at high temperature. The outdiffusion of P from the decomposed In0.5Ga0.5P substrate and agglomeration of Pd and Ge are the primary causes of contact degradation.

Back-Gating Effects on the Ga0.1In0.9P/InP/InGaAs High-Electron-Mobility Transistor.

Pseudomorphic GaInP/InP/InGaAs high electron mobility transistors (HEMT) with improved Schottky contacts and excellent electrical characteristics are grown by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) on the InP substrate. These HEMTs with 1.7 µ m gate length have an average extrinsic transconductance of 225 mS/mm. The back-gating effects of this device structure are investigated for the first time in this structure. Both positive and negative bias are applied to the ohmic and Schottky back-gate contacts of these devices. The positive back-gate bias has no effect on the drain current or the output transconductances of these devices. The effect of the negative back-gate bias is very similar to that when negative bias is applied on the gate of these HEMTs.

Reactive Ion Etch of GaAs and AIGaAs Using BCl 3 , SiCl 4 and SF 6 .Instead of CCl 2 F 2

In the past, CCl 2 F 2 had been widely used in the dry etching process of the GaAs-based materials, However, it causes ozone depletion and is detrimental to the environment. In order to prevent further ozone depletion, it is necessary to search for some substitutedl gases. In this study, chloric gases, like BCl 3 and SiCl 4 , were used to provide an alternative way for the reactive ion etch of GaAs and AlGaAs. To provide high etching selectivity between GaAs and AlGaAs, a fluorine containing gas SF 6 is added, to increase the etch rate of GaAs than that of AlGaAs, which is due to the formation of non-volatile solid AlF 3 . In this study the etching characteristics of the BCl 3 /SF 6 , SiCl 4 /SF 6 were studied and high etching selectivity between AlGaAs/GaAs is achieved.

Cation Source Dependence of Ga0.5In0.5P Growth Rate by Low-Pressure Metalorganic Chemical Vapor Deposition

The Ga0.5In0.5P epilayer was grown by low-pressure metalorganic chemical vapor deposition. Trimethylgallium and triethylgallium were used as the gallium sources, while trimethylindium and ethyldimethylindium were used as the indium sources. The use of triethylgallium incorporated with trimethylindium enhanced the growth rate of Ga0.5In0.5P as compared to incorporation with ethyldimethylindium. While the use of trimethylgallium incorporated with ethyldimethylindium enhanced the growth rate of Ga0.5In0.5P significantly, as compared to incorporation with trimethylindium.