The application of CCl4-doped semi-insulating InP as a buffer layer in a pseudomorphic Ga0.2In0.8P/Ga0.47In0.53As/InP high electron mobility transistor (HEMT) grown by metalorganic chemical vapor deposition is reported. This Al-free InP-base HEMT with a gate length of 1.3 μm has extrinsic transconductances of 420 and 610 mS/mm at 300 and 77 K, respectively. A cutoff frequency of 15 GHz and a maximum oscillation frequency of 40 GHz are obtained. The results demonstrate the CCl4-doped semi-insulating InP is a promising buffer layer for InP-based HEMT. © 1996 American Institute of Physics.published_or_final_versio

Hsu, CC

Ou, HJ

Yang, ES

Yang, YF

Applied Physics Letters

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Title CCl4-doped semi-insulating InP as a buffer layer in GaInAs/InPhigh electron mobility transistorsAuthor(s) Hsu, CC; Yang, YF; Ou, HJ; Yang, ESCitation Applied Physics Letters, 1996, v. 69 n. 8, p. 1143-1144Issued Date 1996URL http://hdl.handle.net/10722/42741Rights Creative Commons: Attribution 3.0 Hong Kong LicenseCCl4-doped semi-insulating InP as a buffer layer in GaInAs/InP highelectron mobility transistorsC. C. HsuDepartment of Electronic Engineering, The Chinese University of Hong Kong, Hong KongY. F. Yang,a) H. J. Ou, and E. S. YangDepartment of Electrical Engineering, Columbia University, New York, New York 10027~Received 18 April 1996; accepted for publication 11 June 1996!The application of CCl4-doped semi-insulating InP as a buffer layer in a pseudomorphicGa0.2In0.8P/Ga0.47In0.53As/InP high electron mobility transistor ~HEMT! grown by metalorganicchemical vapor deposition is reported. This Al-free InP-base HEMT with a gate length of 1.3 mmhas extrinsic transconductances of 420 and 610 mS/mm at 300 and 77 K, respectively. A cutofffrequency of 15 GHz and a maximum oscillation frequency of 40 GHz are obtained. The resultsdemonstrate the CCl4-doped semi-insulating InP is a promising buffer layer for InP-basedHEMT. © 1996 American Institute of Physics. @S0003-6951~96!02234-6#Recently, Gardner et al.1,2 have demonstrated the semi-insulating ~SI! property of CCl4-doped InP grown by lowtemperature metalorganic chemical vapor deposition~MOCVD!. The resistivity of the CCl4-doped InP layer couldexceed 1012 V cm under proper growth conditions.2 TheCCl4-doped InP layer with such a good SI property can re-place the conventionally undoped AlInAs layer or Fe-dopedInP layer in InP-based devices and circuits. The semi-insulating InP layer providing carrier confinement and cur-rent blocking can be used for Schottky barrier enhancementor as the buffer layer in InP-based high electron mobilitytransistors ~HEMTs! and the isolation layer in integrated cir-cuits. Among these applications, the use of SI InP as aHEMT buffer layer may offer some advantages over conven-tional buffer layers. It is well known that Al containing un-doped AlInAs usually used as a buffer layer in InP-basedHEMTs is responsible for trap-related anomalous phenom-ena such as the kink effect, deep levels, and high outputconductance.3,4 An Al-free CCl4-doped InP buffer layer canhopefully eliminate the above effects. Compared to the resis-tivity of 107–109 V cm for MOCVD grown Fe-doped InPlayers,5 the resistivity of the CCl4-doped InP layer can bemuch higher.2In this letter, we present a promising use of CCl4- dopedsemi-insulating InP as a buffer layer in a pseudomorphicGa0.2In0.8P/Ga0.47In0.53As/InP HEMT grown by MOCVD. Itis shown that the kink effect usually present in the InP-basedHEMT is eliminated using the CCl4-doped InP buffer layer.Epitaxial growth was performed in a commercial~Aixtron! MOCVD reactor. Trimethylgallium, trimethylin-dium, tertiarybutylphosphine, and tertiarybutylarsine wereused as the precursors. The CCl4-doped InP buffer layer wasgrown at a CCl4 flow rate of 5 cc/m at temperature of500 °C. The carbon to indium ratio in the gas phase was0.038, while the V/III ratio was 60. The thickness of thebuffer layer is 2000 Å. The HEMT structure and growthcondition are similar to those reported earlier6 except thethickness of undoped GaInAs channel is 400 Å. Since thea!Electronic mail: yfy@ctr.columbia.eduAppl. Phys. Lett. 69 (8), 19 August 1996 0003-6951/96/69(8)/1CCl4-doped InP buffer is a wide gap material, the HEMT isa double heterostructure device. According to Gardneret al.,1,2 the resistivity of the CCl4-doped InP layer dependson both the CCl4 flow rate and the growth temperature. Theresistivity of CCl4-doped InP buffer layer was measured tobe 13107 and 1010 V cm for CCl4 flow rates of 5 and 10cc/m, respectively, which is similar to Gardner’s results. Thehigher CCl4 flow rate gives a higher resistivity at a givengrowth temperature, but it reduces the growth rate due to theetching effect. So the low CCl4 flow rate of 5 cc/m was usedin this work. The fabrication process is similar to that re-ported earlier,6 and the HEMT has a gate length of 1.3 mmand a gate width of 25 mm. The cross section of the HEMTwith the epitaxial layered structure is shown in Fig. 1.Figure 2 shows the typical current–voltage characteris-tics at 300 and 77 K in darkness. Excellent pinch-off char-acteristics are observed. The kink effect related to the qualityof the buffer layer is commonly observed, especially at 77 K,in InP-based HEMT with either an undoped AlInAs buffer3,4or an undoped InGaAs buffer layer.6 In our devices, no kinkeffect is observed at 300 K. The kink effect in the I–V curveat 77 K is hardly noticeable indicating that the CCl4-dopedInP is a promising buffer layer for HEMTs. The drain–source breakdown voltage of 2.5 V is a little bit low due tothe low breakdown voltage of the Schottky gate for thissample. The drain current is slightly photosensitive. There isFIG. 1. Cross section of GaInP/GaInAs/InP HEMT with the layered struc-ture.1143143/2/$10.00 © 1996 American Institute of Physicsa 3% increase in drain current but no kink effect observedunder illumination. The transfer characteristics and the trans-conductance (gm) as a function of the gate bias (Vgs) areshown in Fig. 3 at the drain–source bias of 1.5 V. Thethreshold voltages of 20.85 and 20.75 V were measured at300 and 77 K, respectively. The maximum extrinsic gm of420 and 610 mS/mm are obtained at 300 and 77 K. Thesedata are comparable to those of the InP-based HEMTs withundoped AlInAs ~Refs. 7 and 8! and undoped ~Ref. 9! bufferlayers with a similar gate length.FIG. 2. Drain I–V characteristics of GaInP/GaInAs/InP HEMT withCCl4-doped InP buffer layer at ~a! 300 and ~b! 77 K in darkness.FIG. 3. Drain current (Id) and transconductance (gm) as a function ofgate–source bias at 300 and 77 K.1144 Appl. Phys. Lett., Vol. 69, No. 8, 19 August 1996Microwave measurements were made with an HP8510Bnetwork analyzer and cascade microwave probes in the fre-quency range from 100 MHz to 20 GHz at 300 K. Figure 4shows the current gain and maximum stable gain/maximumavailable gain versus frequency at Vds of 1.5 V and Vgs of20.4 V. The cutoff frequency and the maximum oscillationfrequency are 15 and 40 GHz, respectively. The microwaveperformance can be improved by optimizing the HEMTlayer structure and reducing the gate length.The electron Hall mobility for the HEMT sample wasmeasured to be 4400 and 8400 cm2/V s at 300 and 77 K,respectively. The value of the electron mobility at 77 K isnot as high as expected and the reason is unclear at present.In conclusion, a pseudomorphic Ga0.2In0.8P/Ga0.47In0.53As/InP high electron mobility transistor grown byMOCVD using a CCl4-doped semi-insulating InP bufferlayer is reported for the first time. The dc and rf performanceof the HEMT demonstrates that CCl4-doped semi-insulatingInP is a promising buffer layer for InP/InGaAs HEMTs, al-though the electron mobility and the breakdown voltage ofthe Schottky gate need to be improved.This work was supported by the National Science Foun-dation under Grant No. ECS-93-19987 and by Joint ServicesElectronics Program under Grant No. DAAH04-94-G-0057.The authors wish to thank Q. H. Du for the Hall measure-ments.1N. F. Gardner, Q. J. Hartman, S. A. Stockman, G. E. Stillman, J. E. Baker,J. I. Malin, and K. C. Hsieh, Appl. Phys. Lett. 65, 359 ~1994!.2N. F. Gardner, Q. J. Hartmann, S. A. Stockman, J. E. Baker, and G. E.Stillman, Appl. Phys. Lett. 67, 3004 ~1995!.3 J. M. Dumas, P. Audren, M. P. Favennec, D. Lecrosnier, S. R. Bahl, andJ. A. del Alamo, in the 5th International Conference on InP and RelatedMaterials, April 19, 1993, Paris, France, p. 255.4W. Kruppa and J. B. Boos, IEEE Trans. Electron Devices 42, 1717~1995!.5P. Speier, P. Wiedemann, W. Kuebart, H. Grobkopf, F. Grotjahn, F.Schuler, F. J. Tegude, and K. Wunstel, in Proceedings of the 5th Confer-ence on Semi-insulating III-V Materials, June 1, 1988, Malmo, Sweden, p.295.6Y. F. Yang, C. C. Hsu, and E. S. Yang, Electron. Lett. 30, 1894 ~1994!.7M. Tong, K. Nummila, A. Ketterson, I. Adesida, C. Caneau, and R. Bhat,13, 525 ~1992!.8U. K. Mishra, A. S. Brown, L. M. Jelloian, L. H. Hackett, and J. M.Delaney 9, 41 ~1988!.9A. M. Kusters, A. Kohl, R. Muller, V. Sommer, and K. Heime, 14, 36~1993!.FIG. 4. Current gain ~uh2u! and maximum stable gain/maximum availablegrain ~MSG/MAG! as a function of frequency at Vds of 1.5 V and Vgs of20.4 V.Hsu et al.

CCl4-doped semi-insulating InP as a buffer layer in GaInAs/InP high electron mobility transistors

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CCl4-doped semi-insulating InP as a buffer layer in GaInAs/InP high electron mobility transistors

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