MOVPE Growth of InP-based Heterostructures

Graduate Student: K. Hong
Professor: D. Pavlidis
ARPA/COST MDA972-94-1-0004 and U.S. Army Research Office DAAL03-92-G-0109

The metal organic phase epitaxy (MOVPE) technique is very attractive for the epitaxial growth of compound semiconductors due to its simplicity and flexibility. In addition, the increasing interest in InP and related materials for microwave and optoelectronic devices makes this technique very favorable for their growth, due to its unique capability of growing phosphorus-containing materials. In this work, the growth conditions for InP, InGaAs and InAlAs were optimized and the crystallinity and electrical and optical properties of the materials were characterized using double crystal x-ray diffractometry, Hall measurements and photoluminescence. SIMS and DLTS measurements were also carried out on bulk InAlAs layers and an optimum growth temperature of 650C was found by these techniques.

Iron doping of InAlAs is explored in order to render the buffer and cap layers of InP-based HEMTs less conductive. Ferrocene is employed as iron source and growth is carried out by MOCVD at 650C since this offers minimum deep donor levels according to our DLTS studies. Time-resolved photoreflectancestudies indicated enhancement of deep trap presence with ferrocene flow. Pt Schottky diodes fabricated on such layers show that the electrical properties of InAlAs can be greatly improved up to a certain level of Fe doping.

Record high frequency characteristics have been demonstrated using our in-house MOCVD facility for the growth of InAlAs/InGaAs HEMTs. The results refer to a 1 um-long gate HEMT with fT=60 GHz and fMAX=120GHz and a gain Gmax of 14 dB at 20 GHz.

Isochronal annealing of C-doped InGaAs grown by our MOCVD. The hole concentration is found to increase by a factor of 30 by annealing at 600C for 10 secs. In constrast to C-GaAs, the hole mobility is also found to inrease. The increase of hole mobility could not be attributed to hydrogen depassivation alone but displacement of carbon atoms from C(III) to C(A) site is also suspected.

Heavily carbon doped (6.5e19cm^-3) InGaAs, lattice matched to InP, was grown by LP-MOCVD using all-methyl metalorganics and liquid CCl(4) as a carbon source. The impact of growth conditions on conduction type and alloy composition of InGaAs are studied. The effect of annealing conditions on the hole concentration and mobility of C-InGaAs is investigated and carbon displacement from group III site to arsenic site is suggested as a possible mechanism for the significant increase of hole concentration upon annealing. Base specific contact resistances as low as 5e-7 Ohm cm^2 were demonstrated by depositing Ti/Pt/Au non-alloyed ohmic contacts on annealed base layers.

InAlAs/InGaAs heterostructures were grown for high frequency diode and HEMT applications. In(x)Al(1-x)As/InGaAs(x=0.4, 0.52) heterostructure Schottky diode structures were grown for terahertz multiplier and mixer applications with various epitaxial designs on InAlAs barrier and InGaAs active layers to investigate the effects of epitaxial designs on DC and RF performance of the diodes. These diodes showed promising results for terahertz applications with cutoff frequency as high as 2.6THz. InAlAs/InGaAs HEMTs with an InP buffer were also grown using MOVPE. The fabricated 1um-gate length HEMTs showed DC transconductance as high as 547mS/mm. RF measurements were also performed and showed Gm of 14dB at 20GHz and fTand fMAX of 60GHz and 120GHz respectively, which are among the best results reported with similar gate length.

Current Research Programs: MOCVD

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