Temperature dependence of an InGaAs-2DEG Hall device with large magnetic sensitivity

135

Sensors and Actzmtom A, 40 (1994) 135-M

Temperature dependence of an InGaAs-2DEG large magnetic sensitivity Yoshinobu

Sugyama

EMrochemzcal

Laboratory, l-l-4, Umezono, Tszhba

(Recewed October 25, 1992, m rewed

form

Hall device with

305 (Japan)

February 15, 1993)

Abstract Characterlstlcs of an InGaAs-ZDEG Hall deuce made of pseudomorphlc InAlAs/InGaAs heterostructure semiconductors m the temperature range 10-320 K have been studled This device can be operated with high senstttvtty at low temperature Its magnetic senslttvtty IS several tunes as large as that of InSb Hall dences and the temperature dependence 1s comparable to that of GaAs Hall devices The temperature wefliclents of the Greekcross Hall devtce at room temperature are -0 084 and -054%/K, respectrvely, for current dnve and voltage dnve A maximum magnetic senstttvtty of 33 5 V!T was obtained at 11 K. Powerful sensmg apphcatlons usmg the InGaAs-2DEG Hall device m the demanding condltlons of automobiles and factory automation are expected

1. Iotroduction Semtconductor

magnetic sensors such as Hall devtces

and magnetoresistors are very useful for factory and office automation and home electronics [l] Many Hall devices made of evaporated InSb fihn with high sensit&y are widely used, but their temperature dependence IS large due to a narrow band gap A GaAs Hall device shows a small temperature dependence but lower senslhvlty Recently, highly sensltwe magnetic sensorS made of smgle-heterojunchon sermconductors such as AlGaAs/GaAs [2,3] or InAlAsiInGaAs [4] have been developed The high sensltlvltles of these devices are due to the high electron moblhty of the two-dlmenslonal electron gas (2DEG) confined m the heteromterface The heteroJunctlon sermconductor magnetic sensor 1s expected to find new applications m a cryogemc devxe coupled with a superconductmg device and m hightemperature devices for automobiles or power stations This paper describes the characteristics of the InGaAs-2DEG Hall device m the wde temperature range below room temperature and proposes powerful sensing applications for magneto-optical coupling deaces with LEDs

2. Sample preparation The InGaAs-2DEG Hall devices were made of smgle heterojunction semxonductors grown on semi-msulatmg (100) InP substrates using flux-stabilized molecular

05X24-4247/94/$07 00 8 1994Elsewer Sequoia All nghts reserved SSDI 0924-4247(93)00759-W

beam epltaxy (MEiE) vvlthm a fluctuation of 1% The crystal growth of ternary compound semiconductor was done by the composition control technique wthm an error of 0 03% The growth condihons are reported elsewhere [5] The heterojunchon senuconductor on an InP substrate 1s composed of a buffer layer of undoped In,,Ga,,As (400 nm), a pseudomorphc channel layer of undoped In, 5&,48As (10 nm), a spacer layer of undoped In,,Ga,,As (5 nm), a dopmg layer of 8doped In,, sG% &s (40 nm), and a pseudomorphic cap layer of Sl-doped In,,,Al,,,As (10 nm) The pseudomorphic layer IS thinner than the crltlcal thickness [6] An ohnuc contact was made by alloymg an Au/ NllAuGe film evaporated on the sermconductor Three kinds of InGaAs-2DEG Hall devices, an eight-terminal bndge-shaped element, a four-terminal rectangular element, and a four-terminal Greek-cross element (listed m Table 1) were fabncated by the conventional photohthographlc process wth wet-chemical etchmg All the Hall devices are mounted m a non-magnetic TO5 package A 25 pm diameter Au wire was used with an ultrasomc bondmg machine A photograph of the Greek-cross InGaAs-2DEG Hall device IS shown m Fig 1 The Hall device was put m a metal-shielded cryostat with temperature control m the range 10-320 K and was characterized m a computer-controlled Hall measurement system with a bipolar electromagnet m the range f 15 T A transverse magnetic field was apphed to the sample The planar Hall effect of the heteroJunction semiconductor Hall device can be completely

136 TABLE 1 Specdicatums of expenmental spectmens The Impedance value IS at room temperature Sample no

T84B2

T84Hl

Tg4H2

Tg4I.U

Type of element g=, LXW (run) Hall electrode (pm) Impedance (Cl)

brrdge 1ooox200 20 1450

sq-e 200x200 20 310

rect 400x200 20 650

rect 600x200 20 950

aoss 350x200 200 420

density Let the figure of merit of the magnetic sensltnrlty be defined by usmg matenal parameters as follows M= (KHcLE#~

(2)

or = PI-I(PlW”

Fig 1 Photograph of an InGaAs2DEG Greek-cross Hall device made of pseudomorpluc In0&&4siIn, sGas 2Asheterostructure senuconductor grown on InP substrate by MBE The Hall element LVthe cross shape m the central part of the photograph The length and thewdth of tbc device are350and 200 pm, respectwely The actwe layer thickness IS 10 nm

neglected because the tamer 1s two-dunenslonally confined 111the undoped In, 8Ga,,2As channel layer The band-gap energy of the channel, deduced from the photolummescence spectrum at 4 K, 1s 0 65 eV, wblch IS the same as that of Ge.

(3)

where p 1s the reslstlvlty The product sensitmty can be rewntten by the ratio of the Hall cxxffi~ent to the th&~~ of the actwe layer, f, or by the mverse of the product of the sheet earner density and the electronic charge The figure of ment of the magnetic sensltwlty IS proportional to the Hall moblhty, CL=,the sheet resistance, p/t, and inversely proportional to the sheet carrier density, N,, from eqns (2) and (3) Large values of the Hall mob@ and the Hall coefficient can easily be reahzed m heterostructure semiconductors with a two-dlmenslonal electron gas The Hall mob&y and sheet carrier density of an In, &l,, &/In,,sGa,, A pseudomorphic heterostructure semiconductor gwen by Hall measurement of the bndge-shaped specunen are shown as a function of temperature m Fig 2 The Hall moblhtles at typical temperatures of 10, 77 and 300 K are 116 500, 85 000 and 15 200 cm’/V s, respectively, vvlth sheet tamer densities of 1.38 X lo**, 138 x 10” and 141 X 10” cm-’ Quantlzatlon of the electron gas m the single quantum well IS observed below 100 K. The low-temperature Hall moblhty begms to decrease with T-’ 3 over 50 K and the sheet earner density begms to mcrease with 200,000 r

3. Figure of merit of the magnetic sensitivity The magnetic senslfivlty of a Hall device generally depends on the Hall coefficient for current dnve and on the Hall mobility for voltage drove Rewrltmg the dnve current or voltage as an mput power, P,,, the Hall output voltage of a rectangular Hall element IS ~it=~,((wW@,p,nY~

(1)

where F, IS the geometrical correction factor, w/l the ratio of wdth to length, KH the product sensltrvlty, pH the Hail mobdity and B the apphed magnetic flux

TEMPEAATURE

(KJ

Fig 2 Temperature dependence of the Hall mob&y and sheet tamer density of the heterostructure The Hall mobihty m the range above 50 K 1s dependent on T-’ 3

137

Fig 3 Temperature dependence of the Hall mob&y and sheet tamer density around room temperature The actwatlon energy of the earner m the InAlAs dopmg layer around room temperature IS 10 meV

mdtb ratio for current dnve The geometrical correction factor, F, = (w/l)F[Nw]under a small Hall angle, for voltage drive mcreases with decreasing length-to-mdth ratio, as shown m Fig 5 The expenmental data agree Hnth the theoretical ones The square specimen with large geometrical factor has the largest magnetic sensltw-@, that 1s, 15 V/T for V,,=26 V and Z,,=46 mA at 296 K, and 335 VR for V,,,=225 V and Z,“=54 mA at 11 K The ratios of the magnetic scnsltlvlty at 11 K to that at 296 K are 3 3 and 16, respectively, for low and high electnc fields The d c electric-field dependence of the Hall mobdlty and the sheet tamer density are shown m Fig 6 The mtxal electnc field at the maxmmm curvature of the mobility comcldes Hrlththe muumum of the sheet tamer density The Hall mobility decreases wth an Em2 dependence at a large input The reduction m moblhty 1s pnmanly due to enhanced phonon scattermg [S]

60 -

40 06 20 -

0 10

M=k,pH)'"

ii % -04 s

20

50

loo

200

500

TEMPERATURE(K)

‘Yll__--

4 Flgure of ment of the magnetic scnsltlvlty as a function of temperature

0

05

1

15

2

25

I

3

35

VW

temperature over 270 K. These temperature dependencles around room temperature are shown m detail in Fig 3 The sheet tamer dens@ increases Hnth exp[ - 10 meV/kTj The sheet resistances of the InGaAs2DEG Hall device are 300 and 40 ii/square, respectively, at 300 and 11 K. The figures of ment of the magnetic sensltnrlty of the InGaAs-2DEG Hall device shown m Fig 4 are 26 and 72 (V/A)“%‘, respectively at 300 and 11 K The low-temperature sensitiv&y IS a factor of three better than the room-temperature one. The room-temperature sensltlvlty of this device 1s three tunes as large as that of GaAs and comparable to that of InSb

4. Geometrical efbcts The geometrical dependence of the magnetic sensititmty was mvestlgated using various rectangular Hall devices ~th finger-hke Hall termmals The real Hall output Hrlth the geometrical factor, F,[&v] [7], to an ideal Hall voltage Increases Hrlth mcreasmg length-to-

Fig 5 Geometrical wrrectlon factors of an InGaAs-2DEG rectangular Hall device for voltage dnve at room temperature A large Hall output 1s expected m the square spectmen

200000

;

100000 50000

E S c

20000

;

1: lOOO(

8 i 4

5OOC I-

A,.,

,J

01

-,..I

’

,,(,A

“”

100 1000 1 10 ELECTRICFIELD (V/cm)

Fig 6 D c elecmc-field dependence of the Hall mobihty and sheet earner denalty at operatmg temperatures of 11, 77, 150 and 300 K The Hall mobdlty decreases wth E-’ at large electnc fields The elechw-field dependence above some 100 V/cm seems to be due to Joule heatmg

138

The Joule heatmg has to be considered for a large input power

5. Device

performance of a Greek-cross Hall device

Input and output impedances m the range from 50 to several hundred ohms are needed for matching to external crrcmts A Greek-cross Hall device with a length-to-width ratto of 173 as shown m Ftg 1 has been designed for obtammg the most efficient sensor output [9] The length and wtdth of the devrce are 350 and 200 pm, respectively The devtce impedance IS 420 fl at room temperature The magnetic sensrtivrties of this spectmen are shown m Figs 7 and 8, respectively, for current drtve and voltage dnve wtth temperature as a parameter The offset Hall output, I e , the rmbalance Hall voltage at B =O, IS some 0 1% of the magnetic sensihvity The magnetic sensitivity for current drtve is almost independent of the temperature, but for voltage drive the low-temperature sensitrvtty 1s five tunes as large as the room temperature one The small temperature dependence of the magnettc sensitmty at a constant current of 10 mA IS shown m Ftg 9

g

10:

$

5-

30

50

loo

TEMPERATURE

200 300

500

(K)

Rg 9 Temperature dependence of the magnetic sensltmty of the Greek-cross Hall dewe at a constant current of 10 nk4 The magnetx scnsltmty below 50 K IS larger than that at 300 K by a factor of 25%

220

T84C2 P-

1 20

I0260

5og

0' 10

.

240

TEMPERATURE

(Kl

Ftg 10 Temperature dependence of the magoetlc sensltwty nonnahzed at 290 K of the Greek-cross Hall dewce for current or voltage drive

h 2g Y

1:

:

INPUT CURRENT (mA)

Fig 7 Magnetic sensltwty of the Greek-cross Hall dewce at 11 K and 300 K as a function of mput current

02’ 02

,,I,,.,1 05

1

2

‘I

5

,“I

10

I 20

,’ 50

INPUT VOLTAGE 0

Fig 8 Magnetw senetWy of the Greek-cross Hall dewe K and 300 K as a fun&on of mput voltage

at 11

The relative senstttvtttes for current drive and voltage drive are shown m Frg 10 The temperature coefficient, -0 084%/K, of the magnehc sensrtrvrty for current drrve 1s due to the actrvatron energy of the tamer, 10 meV, tt 1s - 0 54% /K for voltage drrve The temperature coefficient of the reststrvtty 1s 04%/K The maxmmm operatmg temperature eshmated by the band-gap energy of the pseudomorphrc b,Ga,& channel layer, 0 65 eV, is the same as that of Ge The temperature dependence would be improved by the wade-band-gap composrtton and opttmrzatron of the growth condrtrons, such as dopmg mtensrty, etc The InGaAs-2DEG Hall device 1s a htghly-sensmve magnetrc sensor with a high S/N ratro because of Its large magnetrc sensrttvrty [4] and low noise spectrum at audio frequencies [lo] The mmunum detectable magnettc field at dc bras IS =l PT. The magnetic sensttrvrty of an InGaAs-2DEG Hall devtce as a functron of the mput voltage 1s shown m compartson wrth those of commercral Hall devices made of evaporated Mb (HW3OOC)and ion-replanted GaAs (THS107A) m Ftg 11 The stze of these devrces and then geometrrcal

139

05

1

2

5

INPUT VOLTAGE

10

20

50

(V)

Fig 11 Magnetrc senslt~ty of InGaAs-2DEG Hall devws compared wth those of an evaporated InSb Hall dewe and an Ion-implanted GaAs Hall device

phficatlon can be operated by an externally apphed magnetic field The impedance of the Hall devxe driven by a car battery of 12 V IS 600 fi The operatmg current of the Hall device is 20 mA and the magnetic sensitmty IS 10 V/T Applymg an external magnetic field of 0 3 T, the LED is turned on by a Hall output voltage 3 V larger than the threshold voltage It was found that the InGaAs-2DEG Hall device 1s a very powerful magnetic sensor with a high S/N ratio and a small temperature dependence, it 1s even able to be integrated monohthlcally with magnetic sensors and signal-processmg clrcmts composed of low-noise Hall-effect magnetotranslstors

B=03T I----&@

7. Conclusions

12 Powerhd sensing appbcatlon using an InGaAs-ZDEG Greek-cross Hall dewce driven by a 12 V car battery The LED directly connected to the Hall termnAs can be operated by an external magnetic field of 03 T

Fig

factors are almost the same III each case The InSb Hall device has a large magnetic sensltmty but It has

to be operated by a small mput voltage hmlted by the large temperature dependence due to the small band gap The GaAs Hall device can be operated by a large input voltage due to the small temperature dependence, but It has poor magnetic sensltivlty The arrow for the commercial device m the Figure indicates the maxnnum allowable operatmg condltlons below about 100 mW The maxnnum allowable sensltmty of these commercial devices is about 2 V/T, but a very large magnetic sensltltlvlty of more than 10 V/T 1s attamable m the new Hall device made of InAlAs/InGaAs heterostructore sermconductors The magnetic sensitmty of the InGaAs-2DEG Greek-cross shaped Hall device (T84C2) 1s smaller than that of the square Hall device (T84Hl) due to the geometrxal effects shown m Fig 5, but a large output current can be produced by the latter device

6. Proposals for applications A powerful sensmg GaAs-2DEG Greek-cross onstrated m Fig 12 A directly connected to the

application usmg shaped Hall device light-emlttmg diode Hall device without

an In1s dem(LED) any am-

A highly sensitive InGaAs-2DEG Hall device wth a sheet resistance of some 100 a/square made of the pseudomorphlc In, ,,&,&/In, sG~ & heterostructure semiconductor grown on a semi-msulatmg InP (100) substrate has been developed A Hall moblllty of 15 200 cm*/V s Hnth a sheet carrier density of 141 x 10” cm-’ at room temperature was obtamed m the InGaAs-2DEG heterostructure, and there is also a high Hall mobility at low temperature The Hall mob&y decreases with mcreasmg temperature as T-l 3 m the range above 50 K. The number of carriers 1s almost constant below 250 K but increases with mcreasmg temperature mth an activation energy of 10 meV. The temperature coefficients of the magnetic sensltlvlty for current drive and voltage dnve are - 0 084 and - 0 54%/K, respectively A Greek-cross Hall device with a normal impedance of 400 n has a magnetic sensltlvlty larger than that of a commercial InSb Hall device and a temperature coefficient smaller than that of a commercial GaAs Hall device The largest magnetic sensltlvltles of 33 5 and 22 5 V/T, respectrvely, at 11 and 296 K are obtamed for a square Hall device rather than a Greek-cross Hall deuce because of geometrical effects A powerful sensing apphcatlon 1s proposed using a InGaAs-2DEG Greek-cross Hall device drrven by a 12 V car battery to operate an LED under an external applied magnetic field of 0 3 T Various powerful sensmg applications at high temperature and m dirty surroundmgs m factones and automobdes using an InGaAs-2DEG Hall device Hnth high senafivlty and small temperature dependence appear very promlsmg

140

Acknowledgements The author thanks Dr M Tacano of Kyocera Carporatlon for helpful dmsslons, and Mr Y Takeuchl of Nlppondenso Co, Ltd for device fabncatlon

8 W P Hong and P Bhattacharya, HI&field transport m InGaAs/InAlAs modulatmn-doped heterostructures, IEEE Tmns Electron Devtcq ED-34 (1987) 1491-1495 9 J Haeusler and H J bppmann, Hallgeneratoren nut Kleinem Lmeanslerungsfehler, SohdSta~eEIcchon, II (1968) 173-182 10 M Tacano, H Tanoue and Y Sug~yama, Dependence of Hooge parameter of compound senuamductors on temperature, Jpn I App! Phys, 31 (1992) L31CL319

References Y SuByruna, Trends on recent development of senuconductor magnetic sensors,Bull El&m&h Labomloty, 54 (1990) 65-96 Y Suglyama, H Soga and M Tacano. Highly-senslhve Hall element wth quantum-well superlattlce structure, J @s&l Gmw#z, 95 (1989) 394-397 Y Sug~yama, H Saga, M Tacano and HP Bakes, H~gbly senntlve spht-contact magnetoreslstor with AL4s/GaAs superlattIce structures, IEEE Trans Electron Devrces, ED-36, (1989) 1639-1643 Y Supyama, Y Takeucln and M Tacano, H&y-sensttnre InGaAs-2DEG Hall device made of pseudomorplnc In,,Al,,&s~~ *Ga,,& heterostructure, Sensors and Actuator.. A, 34 (1992) 131-136 Y Suglyama, Y Takeuchl and M Tacano, l-i@ electron mob&y pseudomorpbx In&&,&./InasGa,&s heterostructure on InP grown by flux-stabdlzed MBE, J Cqwml Grwrh, 115 (1991) 509-514 M Tacano, Y Sugryama and Y Takeuctn, Cntical tlnckness of a pseudomorphrc IssG%& heterostructure grown on InP, Appl Phys Len, 58 (1991) 2420-2422 H Ltppmann and F Kulxt. Der Geometneemfluss auf den Hall-Effekt be] rechtecklgen Halblelterplatten, 2 Natut$orxch , I3a (1958) 474-483

Biography YoshznobuSugryama was born m Glfu, Japan, m 1945 He received B SC and M SC degrees m fine measurement engmeenng from Nagoya Institute of Technology m 1968 and 1970, respectively, and the Ph D degree m physical electromcs from the Tokyo InsWute of Technology 1111984 In 1970, he jotned the Electrotechmcal Laboratory, Mmlstry of International Trade and Industry, Japan, where he has been workmg on sermconductor magnetic sensors He was a Wsamg Scholar at the Umverslty of Cahfomla, Berkeley, durmg 1981-1982, workmg on semxonductor-coupled superconductmg devices HW current research mterests mclude quantum-effect sensors and microwave devices with InP-based heterostructure senuconductors Dr Supyama 1s a member of the Apphed Physxs Society of Japan, the IEE of Japan and the IEICE of Japan