A7_The Novel InAsGaAs High Lattice Mismatch Strained Layer Growth

8/9/2019 A7_The Novel InAsGaAs High Lattice Mismatch Strained Layer Growth

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The Novel InAs/GaAs High Lattice MismatchStrained Layer Growth

Chih-Chin YangDepartment of Microelectronics Engineering, National Kaohsiung Marine University,

Kaohsiung, 811Taiwan, Republic of [email protected]

The i-GaAs buffer layer is grown on (100) semi-insulated GaAs substrate at600 by mole fraction ratio of group V and group III( V/III mole fraction ratio) of 50optimum. The growth rate of GaAs layer is 0.11 m/min . The n-like InAs layerformed high strained layer is grown on GaAs buffer layer at substrate temperature of600 by V/III m ole fraction ratio of 50 optimum also. The interface region ofGaAs and InAs layer possessed high strained. The growth time of InAs layer can notbe exceeded 20 minute consequently. The growth rate of InAs layer is about 0.12m/min at growth temperature of 600 . Due to the strained effect, the banddiagram of InAs/GaAs heterostructure will be changed.

Keywords: GaAsInAs Strained LayerLattice mismatch

/

[email protected]

GaAs(100) GaAs 600V/III

50GaAs0.11 m/minn-like InAs GaAs 600V/III50GaAs/InAs InAsGaAs0.12m/min/

(Keywords)(Keywords)(Keywords)(Keywords):::://


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1. IntroductionThe GaAs material is belong to

zincblende structure [1-3] and the active energyEA of Ga and As in GaAs material are6.0ev and

3.2ev, respectively[4-8]. The lattice constant ofGaAs material is about 5.65325 at 300K[1-3]and the energy band type of GaAs belong to

direct band gap[4]. The GaAs material possessedlight effective mass, so the electron mobility islarger [9]. So as to GaAs material can be appliedin higher frequency devices as like resonanttunneling diodes (RTD) [10-14], photodetectors[15-18], heterostructure bipolar transistor(HBT)[19-20], high electron mobility transistor(HEMT) [21-22], and Laser diodes [23-25] etc.The InAs material belonged to zincblendestructure also. The lattice constant of InAsmaterial is about 6.0584 at 300K, and theenergy band type of InAs compound is directband structure [4-8]. The InAs materialpossessed not only wider energy band gap but

also much higher electron mobility about 30,000cm2/VS and lower LO phonon about 29.6mev at room temperature than other III-Vsemiconductor compounds[1-3]. The compoundof GaAs and InAs semiconductor called Inx

Ga1-xAs combined the all merits of GaAs

material and InAs material characteristics, so theInxGa1-xAs/GaAs devices have been

comprehensively grown and applied recently[10-25]. Because the difference of energy band(Eg) between InGaAs and GaAs material issmaller than that between InAs and GaAsmaterial about 1.06 ev, we studied the InAs

material grown on the GaAs material formedtype I structure. The higher barrier height ofInAs/GaAs heterostructure will result inexcellent devices characteristic perfectly, if thestrain effect of InAs/GaAs heterojunction can beovercome. The functions of InAs/GaAs quantumwell or superlattice devices will much better. Westudied the bulk characteristics of InAs/GaAshigh lattice mismatch here by using metalorganic chemical vapor deposition growthmethod (MOCVD).

2. Experimental system and proceduresThe InAs/GaAs heterostructure is grown

by MOCVD system. This system including thereaction chamber system, the exhausted system,the gas handling system, and the automaticpressure control(APC) system. The reactor isdesigned by horizontal type chamber constructed

with a rectangular cross section(2.52 cm2) anda water cooling jacket on the top of growth zone.The susceptor was made of Mo with an area of 5

2 cm2 and 5 titled angle which can provideuniform growth rate crossing the substrate. The

exhausted system is composted by the one turbopump and two rotary pumps. The two rotarypumps are connected with main line system andbypass line system, respectively. The turbopump is connected with main line system thatcan keep the pressure of reactor, in order toimprove the growth quality of the film. In the

gas handling system, under 10-3 Torr thepalladium-diffused H2 was used as the carrier

gas and the purge gas. The H2 is send to the

reactor system after H2 is purified by 0.5 m

particle filter, the removing oxygen, the moisterfilter, and the H2 purifier containing palladium

at the operating temperature range of 370 to400 . The automatic pressure control systemcan stabilize the pressure of growth systemduring the growth process. It consists of apressure sensor, a pressure display, a pressurecontroller, and an exhaust throttle valve.

The growth temperature and pressure of

InAs/GaAs is about at 600 and 150 Torr,respectively. Thriethylgallium (TEGa) andtrimethylindium (TMIn) bubblers weremaintained at 10 and 20, respectively. Theconcentration of arsine (AsH3) with hydrogen is

15.1%. The cross section schematic ofInAs/GaAs bulk growth is shown in Fig.1. Inthis work, we studied the characteristics ofInAs/GaAs bulk material by changing the V/IIImole fraction ratio of InAs material and thegrowth time of InAs layer.

n-Like InAs

Strained LayerThickness of 50n-Like GaAs

Strained LayerThickness of 60

(100) GaAsInstrinsic Subtrate

Fig.1 The cross section schematic of high strainInAs/GaAs structure.

The surface morphology of InAs bulklayer is viewed by optical electron microscopyfor various differential V/III mole fraction ratio

and growth time of InAs material. The growthrate of InAs bulk layer grown on GaAs bufferlayer is measured by scanning electronicmicroscopy from the cross section of InAs layer.The x-ray diffraction can see the quality of InAsl a y e r b y j u d g e o f f u l l w i d t h h a l f maximum(FWHM). The quality of InAs layergrown on GaAs mater ia l can be a lsounderstood by x-ray diffraction Laue pattern.


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3. Results and DiscussionsThe mole fraction ratio of group V and

group III so called V/III ratio is important, forgrowth InAs strained layer on the GaAs layer.We calculated the V/III ratio, as follow

RM

M

V

III

==== (1)

M FX P

P PIII fs

III

G III

====

100(2)

log( )P BA

TIII ==== (3)

M FY

CV fs N==== 100 (4)

where R V/III mole fraction ratio.MIII mole value of group III.

MV mole value of group V.

Ffs full scale of flow meter in

group III or group V.

X,Y group III and group V vaporflow values of flow meterduring growth.

CN gas concentration of group

V source(15.1 in AsH3).

PG pressure of growth chamber.

PIII partial pressure of group III

in the bubbler.A,B constants for different material.

(A=8.224, B=222 for Gallium)(A=3014, B=10.52 for Indium)

T bubbler temperature of group

III ().We can obtain the V/III ratio by

substitution (3) into (2) and then substitution (2)and (4) into (1).

(a) Optical electron microscopyThe surface morphology of InAs

layer grown on GaAs material is viewed byoptical electron microscopy in multiplication of500 times. We can study the different surfacemorphology of InAs layer at the various growthparameters. The strained effect and optimumgrowth conditions will be able to understand

slightly for InAs compound grown on GaAslayer by optical electron microscopy.The GaAs buffer layers are grown by

V/III ratio of 50 optimum value at substratetemperature of 600 in 30 minutes for allInAs/GaAs heterostructure. The surfacemorphology of InAs structures layer grown onGaAs buffer layer is shown in Fig.2. Making acomparison with Fig.2(a), 2(b), 2(c), and 2(d),we can understand that when thickness of InAsstrained layer is thick in longer growth time, the

surface morphology of InAs is found rough.Because of dislocation defects of InAs/GaAsinterface resulting in strained effect, the danglingbond of InAs and vacancy defects result in theimpurity autodoping in the institute defect forweak As-ionic bond. The thicker the strainedlayer is, the more serious the phenomenon is. So

the optimum growth time of InAs strained layergrown on GaAs substrate at growth temperatureof 600 is less than 20 minute. This result canbe fit by growth rate of InAs and the relationship

between critical thickness LC and latticeconstant a of InAs given[26] by

]12

[ln)1(2144.0

)4

1(+

+

=

a

La

L C

p

p

C

(5)

where P is the Poisson's ratio which usuallyequals to 1/3. In Fig.3, the surface morphologyof InAs layer is shown for different V/III ratiovalue at the same buffer layer growth condition.The GaAs buffer layer are grown by V/III ratioof 50 and in 30 minute at substrate temperatureof 600. The InAs strained layer grown onGaAs buffer layer are grown by three kind V/IIIratio and all in one hour at growth temperatureof 600 . The surface morphology is roughWhen the V/III ratio is less than 5, due to theGa-rich resulting in vacancy defect. The surfacemorphology is smooth and have a little of blackspots when the V/III ratio is larger than 75, due

to the As-rich slightly resulting in institute defect.So the optimum V/III ratio value of growth InAsstrained layer is about 50.

(a) (b)

(c) (d)Fig.2 The surface morphology of InAs strain

layer grown on GaAs buffer layer at Tgrow=600 by V/III ratio of 50 in growth timeof (a) 20 min., (b) 40 min., (c) 1 hr., and (d)


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1 hr. 40 min.

(a) (b) (c)Fig.3 The surface morphology of InAs strainlayer grown on GaAs buffer layer of V/III ratioof 50 and in 30 minute at Tgrow=600 by V/IIIratio of (a) 5, (b)50, and (c)75 in one hour.

(b) Scanning electron microscopy(SEM)Fig.4 is clearly appeared the cross section of

InAs/GaAs structure by scanning electronmicroscopy without using chemical etching. Thestructure is fabricated by growth GaAs bufferlayer on (100) semi-insulated GaAs substrate atsubstrate temperature of 600 in V/III ratio of50 firstly. Then the InAs compound is grown byV/III ratio of 50 at growth temperature of 600on GaAs buffer layer that already grown onGaAs substrate before. From the cross sectionphotography of InAs/GaAs heterostructure byscanning electron microscopy of multiplicationof 1000 times, we can found the thickness ofGaAs buffer layer about 2.2m in growth timeof 30 minute and of InAs strained layer about2.392 m in growth time of 20 minute.According to the growth dynamic mechanism,the experimental values of growth thickness ofInAs strained layer and GaAs buffer layer arecorrespond to the calculated. From the Fig. 4, the

growth rates of GaAs buffer layer grown on

GaAs

InAs

Fig.4 The cross section of InAs/GaAs structureby scanning electron microscopy.

GaAs substrate and InAs strained layer grown onGaAs buffer layer are about 110/mm and

119/mm, respectively. Although the InAsmaterial possessed larger lattice mismatch thanGaAs material grown on GaAs substrate, thegrowth rate of InAs strained layer on GaAs layeris larger than that of GaAs buffer layer on GaAssubstrate at the same growth conditions. Thereason is that the active energy of In-source is

larger than that of Ga-source with As-source.Unstrained Strained

GaAs InAs GaAs GaAs InAs

GaAs

ECEC

HH

LH, HH

LH

Fig.5 The energy band representation of aGaAs/InAs/GaAs single quantum well withand without the influence of strain.

4. ConclusionsBecause of the high strain effect between

InAs layer and GaAs layer, the InAs can not begrown too thick on GaAs layer, shown in Fig.5.The quality of InAs layer is much better for highV/III ratio than for low V/III ratio. The qualityof GaAs layer is influenced by V/III ratio also.The strained effect will influence the band

structure of InAs/GaAs surely. The strainedeffect of GaAs/InAs/GaAs heterostructurebelongs to compression strained effect.

5.AcknowledgementThis work was supported by National

Science Council under Contract NSC-93-2745-E-022-001.

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A7_The Novel InAsGaAs High Lattice Mismatch Strained Layer Growth