Rapid Thermal Alloyed Ohmic Contacts to p‐Type GaAs

Abstract

A systematic study of Au/Zn/Au ohmic contacts to Be‐implanted p‐type normalGaAs by rapid thermal alloying is presented. The processing conditions, such as zinc composition and temperature‐time cycle, are optimized. For the peak hole concentration, about Nnormala=3×1017 cm−3 , contact resistivity as low as 3.3×10−6 normalΩ cm2 is obtained. The microstructure of the contact is investigated using SEM, EDXA, AES, and XRD measurements in order to explore the correlation of the structural information with electrical characteristics represented by contact resistivity. It is found that during alloying, the normalGaAs layer near the interface is decomposed due to Ga and As outdiffusion, enhanced by Au interdiffusion. Ga diffuses to the contact surface in a much larger extent than As does. The interaction of Au and Ga, which produces α‐normalAuGa phase, plays a key role in the formation of alloyed ohmic contacts to normalGaAs . The rapid thermal processing technique provides better control of Au‐Ga reaction, as well as limited dissolution of the normalGaAs surface, which makes the optimum ohmic contact possible. The present work has demonstrated that rapid thermal alloying offers obvious advantages over the conventional furnace alloying process, including lower contact resistivity, better interface morphology by limiting interfacial liquid phase reaction, and controlled shallow penetration depth.

Ohmic contacts fabricated on moderately doped p-type GaAs by sputtering deposition and a laser-firing process

“…4,5 The first Au (20 nm) layer is designed to provide good adhesion of the Zn layer and its relative thinness should permit easy penetration of Zn into the GaAs bulk during the alloy process. The Zn (50 nm) layer is the doping source to create the tunneling ohmic contact.…”

“…The thickness of the Zn layer was fixed at 50 nm, based on previous studies. 4,5 Sputtering conditions for each sample are summarized in Table II. The fabrication process was conducted as follows:…”

“…(4) Rapid thermal annealing: This step was performed based on the conditions reported in a previous work. 4 Figure 3(b) shows the equivalent resistance of a structure after the RTA step. The total resistance can be calculated using the following equation:…”

“…Aubased alloys are the materials most commonly used for both n-and p-type GaAs, 3 with Au/Zn/Au, 4,5 AuBe, 6 and Ti/Pt/ Au (Ref. 6) contacts being the most common on p-type GaAs.…”

Polarity driven simultaneous growth of free-standing and lateral GaAsP epitaxial nanowires on GaAs (001) substrate

“…To understand this finding, the initiation of the nanowire growth should be clarified. In this regard, we note that (1) GaAs near the Au/GaAs interface can decompose due to Ga and As outdiffusion enhanced by Au interdiffusion at a annealing temperature over 350 C, 28 and (2) Au and Ga would form a liquid alloy, while As atoms evaporate when the temperature approaches 600 C. 29 In a study of annealing Au-coated GaAs (100) substrate at 450 C for 3 h, square or rectangular pits were found on the GaAs surface. 30 Accordingly, we anticipate that annealing the GaAs (001) substrate with Au nanoparticles at 600 C leads to the incorporation of Ga into the Au particles which then etches the GaAs (001) substrate directly under the particles to form the upside-down pyramids, as schematically illustrated in Figs.…”