P. M. Thomas

Pt/Ti/p‐In0.53Ga0.47As low‐resistance nonalloyed ohmic contact formed by rapid thermal processing

Very low resistance nonalloyed ohmic contacts of Pt/Ti to 1.5×1019 cm−3 Zn‐doped In0.53Ga0.47As have been formed by rapid thermal processing. These contacts were ohmic as deposited with a specific contact resistance value of 3.0×10−4 Ω cm2. Cross‐sectional transmission electron microscopy showed a very limited interfacial reacted layer (20 nm thick) between the Ti and the InGaAs as a result of heating at 450 °C for 30 s. The interfacial layer contained mostly InAs and a small portion of other five binary phases. Heating at 500 °C or higher temperatures resulted in an extensive interaction and degradation of the contact. The contact formed at 450 °C, 30 s exhibited tensile stress of 5.6×109 dyne cm−2 at the Ti/Pt bilayer, but the metal adhesion remained strong. Rapid thermal processing at 450 °C for 30 s decreased the specific contact resistance to a minimum with an extremely low value of 3.4×10−8 Ω cm2 (0.08 Ω mm), which is very close to the theoretical prediction.

Interfacial microstructure and electrical properties of the Pt/Ti ohmic contact in p-In0.53Ga0.47As formed by rapid thermal processing

The interfacial microstructure and electrical properties of the Pt/Ti ohmic contact to p‐In0.53Ga0.47As (Zn: 5×1018 cm−3) formed by rapid thermal processing (RTP) were intensively studied. Significant interdiffusion of Ti, In, and As across the interface, driven by RTP, occurred at temperatures of, or above, 350 °C for a heating duration of 30 s. A minimum specific contact resistance (9.0×10−6 Ω cm2) was achieved after heating at 450 °C. Cross‐sectional transmission electron microscopy of this sample revealed an interfacial reaction zone with complicated microstructure, and the dominant interfacial compound was identified to be InAs. Further increase in RTP temperature resulted in a change in the microstructure, and degradation of the contact resistance. The temperature‐dependence characteristic of the specific contact resistance of as‐deposited Pt/Ti contact to InGaAs revealed a thermionic‐emission‐dominated carrier‐transport mechanism with an effective barrier height φb, of 0.13 V. RTP treatment to the ...

Pt/Ti Ohmic contact to p++‐InGaAsP (1.3 μm) formed by rapid thermal processing

Nonalloyed Ohmic contacts of evaporated Pt/Ti to p‐InGaAsP (λg=1.3 μm) with different Zn doping levels ranging 5×1018–2×1019 cm−3 have been fabricated by rapid thermal processing. These contacts showed Ohmic behavior prior to any heat treatment with a specific contact resistance of 4×10−3 Ω cm2 for the lowest doping level and 1×10−4 Ω cm2 for the highest level. A decrease in the specific resistance was achieved by supplying rapid thermal processing to the contacts, while the lowest values were observed on all the contacts as a result of heating at 450 °C for 30 sec. The lowest resistance of 1×10−6 Ω cm2 was achieved at the contact that was formed on the 2×1019 cm−3 Zn‐doped InGaAsP layer. Measurements of the conduction activation energy yields a good linear dependence of the specific resistance on temperature in all the contacts as deposited and after the different heat treatments. The higher the doping level and the rapid thermal processing temperature up to 450 °C, the lower the activation energy, which...

Pt/Ti/n‐InP nonalloyed ohmic contacts formed by rapid thermal processing

Low resistance nonalloyed ohmic contacts of e‐gun evaporated Pt/Ti to S doped n‐InP 5×1017, 1×1018, and 5×1018 cm−3 have been fabricated by rapid thermal processing. The contacts to the lower doped substrates (5×1017 and 1×1018 cm−3) were rectifying as‐deposited as well as after heat treatment at temperatures lower than 350 °C. Higher processing temperatures stimulated the Schottky to ohmic contact conversion with minimum specific contact resistance of 1.5×10−5 and 5×10−6 Ω cm2, respectively, as a result of rapid thermal processing at 450 °C for 30 s. Heating at a temperature of 550 °C again yielded a Schottky contact. The contact to the 5×1018 cm−3 InP was ohmic as deposited with a specific contact resistance value of 1.1×10−4 Ω cm2. Supplying heat treatment to the contact caused a decrease of the specific contact resistance to a minimum of 8×10−7 Ω cm2 as a result of rapid thermal processing at 450 °C for 30 s. In all cases, this heat treatment caused a limited interfacial reactions between the Ti and t...

AuBe/p‐InGaAsP contact formed by rapid thermal processing

Alloyed ohmic contacts of AuBe (1% Be by weight) to 5×1018 cm−3 Zn‐doped p‐InGaAsP (λg=1.3 μm) were fabricated by rapid thermal processing and its performance was compared to those of the contacts formed by conventional furnace heating. The specific contact resistance decreased from a value of 4.9×10−4 Ω cm2 as‐deposited to a value of 4.9×10−7 Ω cm2 as a result of rapid thermal processing at 420 °C for 30 s. This value was much lower than the value of 3.9×10−6 Ω cm2 obtained as a result of furnace heat treatment at 420 °C for 10 min. Rapid thermal processing at higher temperatures caused a sharp increase of the specific contact resistance. Auger depth profiling indicated that the degradation of the contact electrical performance at temperatures of 450 °C or higher were caused by intensive localized interactions between the AuBe and the InGaAsP and out‐diffusion of all the quaternary elements toward the surface of the contact. The effective stress in the alloyed layer, normalized to the initial AuBe thickn...

SiO2 mask erosion and sidewall composition during CH4/H2 reactive ion etching of InGaAsP/InP

SiO2 mask erosion has been studied during CH4/H2 reactive ion etching of InGaAsP/InP double heterostructures. The amount of mesa mask narrowing at a pressure of 100 mT, normalized for an etch depth of 3.5 μm, is approximately 0.4–0.6 μm and decreases slightly with increasing self‐bias voltage. It is not strongly dependent on the sidewall angle of the mask or CH4 concentration. Mask residue deposits on the etched sidewall under conditions of relatively high CH4 concentration and low power density. Auger electron spectroscopic analysis of the sidewall shows that the deposit contains a significant amount of elemental Si, which suggests a mechanism for mask erosion in which SiO2 is reduced to Si in the hydrogen/hydrocarbon‐rich environment of the plasma.

Growth of InGaAs/InP quantum well structures by low-pressure metalorganic chemical vapor deposition

Abstract We have successfully grown InGaAsP/InP single quantum well (SQW) and multi quantum well (MQW) structures by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The LP-MOCVD reactor is a commercial unit built by AIXTRON GmbH, the first of its kind in the United States. The quantum wells grown in this reactor consist of 1.3 and 1.5 μm composition InGaAsP, with barriers of InP. Layer thicknesses vary from 18 A to 1300 A for the various structures grown. Analysis of these structures by low-temperature photoluminescence reveals distinct, sharp luminescent peaks, with half-widths from 4.8 meV to 13 meV. Cross-sectional transmission electron microscopy and Auger spectroscopy of the quantum well structures reveal extremely sharp interfaces and homogeneous composition, demonstrating the feasibility of LP-MOCVD for the growth of very thin epitaxial layers. These preliminary data indicate that the growth of MQW structures for the next generation of laser diodes (i.e. MQW-DFB lasers), with monolayer interfacial abruptness, is possible by LP-MOCVD.

Growth of InGaAsP/InP single‐quantum‐well and multiple‐quantum well structures by low‐pressure metal‐organic chemical vapor deposition

InGaAsP/InP single‐quantum well and multiquantum‐well (MQW) structures have been successfully grown by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD). The quantum wells grown consist of 1.3‐ and 1.5‐μm composition InGaAsP, with barriers of InP. Layer thicknesses vary from 18 to 1300 A for the various structures grown. Analysis of these structures by low‐temperature photoluminescence reveals distinct, sharp luminescent peaks, with half‐widths from 4.8 to 13 meV. Cross‐sectional transmission electron microscopy (XTEM) and Auger spectroscopy of the quantum‐well structures reveals extremely sharp interfaces and homogeneous composition, demonstrating the feasibility of LP‐MOCVD for the growth of very thin epitaxial layers. This preliminary data indicates that the growth of MQW structures for the next generation of laser diodes (i.e., MQW‐distributed‐feedback lasers), with monolayer interfacial abruptness, is possible by LP‐MOCVD.

Metallic tungsten phosphide films formed by spin coating peroxopolytungstic acid on InP

Metallic β‐WP2 films have been formed on InP by reacting amorphous peroxopolytungstic acid (APA) films on InP in a PH3/H2 ambient at 600 °C. The resulting metallic film exhibits a low sheet resistance (310 μΩ cm) and preliminary measurements suggest the contact on n‐InP is ohmic. By using the unreacted peroxopolytungstic acid films as a negative inorganic photoresist, patterned β‐WP2 metallic films on InP have been made without the use of a separate metal film etching step. The reacted metallic films show a smooth, abrupt metal/semiconductor interface. The high temperature stability of β‐WP2 on InP suggests that this material may be useful as a refractory contact to InP.

Process Design for Non-Alloyed Contacts to InP-Based Laser Devices

Pl/Ti and W thin films on n- and p- type InP and related materials have been investigated for potential use as a refractory ohmic contacts for conventional, single-side coplanar contacted and self-aligned barrier hetcrostructurc laser devices. Pt and Ti films were deposited sequentially by electron gun evaporation, while the W layer was rf sputtered, both onto p + -In 0.53 Ga 0.47 As (Zn doped 5×l0 18 cm −3 ) and n − - InP (S doped, 5×l0 18 cm −3 ). The deposition parameters of the two metal systems were optimized to produce adherent films with the lowest possible induced stress. Almost all the studied systems performed as ohmic contacts already as-deposited and were heat treated by means of rapid thermal processing in the temperature range of 300–900°C. The final contact processing conditions were tuned to provide the lowest possible contact resistance values accompanied by low mechanical stress and stable microstructure.