InP-Based Metalorganic Chemical Vapor Deposition (MOCVD) Material and HEMT, HBT Device Studies

With the acquisition of a new Metalorganic Chemical Vapor Deposition (MOCVD) system (EMCORE GS3200) by our group, our activities expanded to basic material studies as necessary for the development of high-performance electronic and optoelectronic devices and demonstration of novel concepts using such devices. The goal of our program in this area is to study and optimize the basic properties of materials such as InP, InGaAs and InAlAs, while at the same time being driven by our device needs. Thus, not only is basic material understanding possible, but demonstration of the material capabilities can also be made using device needs as the driving force of our research. Our work has benefited extremely from national and international collaborations established in the area of characterization of our materials. We are currently working on the use of these materials for HEMT, HBT and THz-diode applications.

The following summarizes our MOCVD material research achievements in this area:

MOCVD Highlights of InP-Based Materials

• InAlAs background carrier concentration

• Electrical properties of InAlAs

• Heavily carbon-doped InGaAs

• Evaluation of deep levels in unintentionally doped InAlAs grown by MOCVD and demonstration of two different origins for the residual carrier concentration: (i) deep donor located at Ec-(0.13+-0.04)eV for growth at low temperatures, (ii) preferential incorporation of shallow donor attributed to Si at higher growth temperatures.

• Demonstration of no correlation between oxygen content and electrical characteristics of MOCVD grown InAlAs.

• Evaluation of optimum temperature for InAlAs MOCVD growth. A temperature of 650 C was selected in order to minimize trap effects, while at the same time achieving minimum background concentration and reduced gate leakage. Best PL and x-ray characteristics are also demonstrated for InAlAs at the same growth temperature.

• Demonstration of higher transport efficiency without impact on InAlAs material quality using reduced AsH3 flow and susceptor rotating speed in MOCVD growth. This permitted improved uniformity, reduced source consumption and less equipment maintenance.

• Demonstration of record microwave characteristics from in-house MOCVD grown 1um long-gate InAlAs/InGaAs HEMTs (fT=60 GHz, fmax=120 GHz).

• Demonstration of the impact of temperature nonuniformity and reactor geometrical effects on InAlAs spectral uniformity using spectrally resolved scanning photoluminescence (SPL) techniques. The results showed that reduced rotation speed degrades the compositional uniformity due to changes in temperature uniformity. However, reduced rotating speed improves the hydrodynamic patterns and offers a flatter boundary layer with the result of more uniform thickness across the wafer.

• Demonstration of thermal degradation of the InAlAs/InP interface and of the InP buffer at temperatures lower than the optimum deposition temperature for InAlAs. This led to the need for growth conditions selection by making a slight compromise in InAlAs characteristics.

• Demonstration of carbon-doped InGaAs lattice matched to InP using all-methyl metalorganics and liquid CCl4 as a carbon source. Low growth temperature (< 500C) and V/III ratios (~5) were used to obtain p-type material. Both the TMGa and TMIn incorporation efficiencies are reduced with CCl4 presence in contrast to previously published gaseous CCl4 results. Insensitivity of alloy composition of C-InGaAs to the amount of CCl4 is shown at low growth temperatures.

• Demonstration of heavily carbon doped p-InGaAs of the order of 6.5x10^19cm^-3 using TMIn, TMGa and liquid CCl4.

• Demonstration of very low base contact resistance (5x10^-7 Ohm cm^-2) for InP/InGaAs HBTs using C-doped base layers grown with TMGa, TMIn and liquid CCl4.

• Demonstration of reduced photo-carrier lifetime and thus deep trap enhancement by increased iron doping of InAlAs. Ferrocene was used as iron source of the MOCVD grown InAlAs layers and time-resolved photoreflectance was employed for characterization.

• Demonstration of improved electrical characteristics (increased resistivity and larger Schottky breakdown) for increased iron incorporation in InAlAs. Degradation of the electrical characteristics was observed beyond a certain level of ferrocene flow due to iron precipitates.

Technical Developments

Review of Group Activities