ELECTRONS AND HOLES IN InAs-Ga (Al) Sb (As) QUANTUM WELLS

HAL Id: jpa-00226733

https://hal.archives-ouvertes.fr/jpa-00226733

Submitted on 1 Jan 1987

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

ELECTRONS AND HOLES IN InAs-Ga (Al) Sb (As) QUANTUM WELLS

H. Munekata, T. Smith, F. Fang, L. Esaki, L. Chang

To cite this version:

H. Munekata, T. Smith, F. Fang, L. Esaki, L. Chang. ELECTRONS AND HOLES IN InAs-Ga (Al) Sb (As) QUANTUM WELLS. Journal de Physique Colloques, 1987, 48 (C5), pp.C5-151-C5-154.

�10.1051/jphyscol:1987529�. �jpa-00226733�

ELECTRONS AND HOLES IN InAs-Ga(Al)Sb(As) QUANTUM WELLS'"

H. MUNEKATA,

S M I T H , 111, F.F. FANG, L .

and L . L . CHANG IBM Thomas

W a t s o n R e s e a r c h Center, P.O. Box 218, Yorktown H e i g h t s , N Y 10598,

Quantum wells composed of type-11 heterojunctions of InAs-Ga(N)Sb(As) ternary alloys have been prepared by molecular beam epitaxy as an extension of the binary InAs-GaSb. By increasing the alloy compositions, the nature of the conduction changes from semimetal-like to that of a single canier. For the semimetallic quantum wells, the magneto-transport behaviors reflect the change in

densities, leading to the adhilation of holcs at high magnetic fields.

Spatid separation of electrons and holes is one of the fundamental features in the typc-I1 hetcrojunctions.

Because of its extreme band edge configuration of InAs-GaSb heterojunction[I], these two

expected t o coexist in channels parallel to the heterointerface. Several works have been carried out, as motivated by the interesting situation, although the precise origin of the coexisting

still remains largely unknown[2,3]. In this paper, we report the properties asociated with the transition between semimetallic and semiconducting situations in Ids-GaSbAs and InAs-GaAlSb quantum wells. With these structures, both d e r densities have been mntrolled by changing the alloy compositions, providing either electron-hole or single electron conduction with high electron mobiities over 1(Ycm2/V.sec . In the quantum wells where conduction is semimetal-like, the transition bctwecn the electron-hole and

single electron

occurs by the application of a high magnetic field. Complete aMihilation of holes is achieved when the lowest hole Landau level crosses the Fermi level.

Figure 1 illustrates what we expect for the band edges when the GaSb layers are alloyed by the replacement of either group 111 (cation site) or group V (anion site) element. We have both electron and hole channels for the U s - G a S b biiary junctions, as shown in Fig.l(a), where the GaSb valence band edge k2 lies above the lnAs conduction band edge E,, . Nloying the GaSb laym moves the valence band edge E,, downward with respect to the conduction band edge E, (Fig.1 (b)

Finally, the two band edges cross (Fig.1 (c)), and the semimetallic channels disappear. T o study this, two series of quantum wells, namely GaSbAs/lnAs/GaSbAs and GaNSb/lnAs/GaAlSb, werc prepared by molecular beam epitaxy on semi-insulating GaAs(100) substrates at 550"C[4]. The lnAs layer thickness was kept constant at 20nm. The alloy compositions range from 0 to 0.2 for x, and 0 to 0.5 for y, in the GaSb,-,As, and the Ga,_,QSb, respectively.

Figure

shows the typical magneto-tnnsport spectra for InAs-Ga,_,AI,Sb quantum wells. As clcarly seen, the complex behavior characteristic of thc biiary InAs-GaSb we11[2.3] gradually disappears with increasing

composition y. Consequently, the spectrum at y-0.3 is quite similar to that of a single carrier systcrn. This situation corrcsponds to the quantum well structure with the band cdgc profile illustrated in Fig. I (c). l'hc same trcnd has also been observed for the Ids-GaSb,.,A$ quantum wells in that the transport characterictic changes from the complex

("~ork supported in part by the U.S. Army Research O f f i c e . The high-field measurements were performed at the Francis Bitter National Magnet Laboratory

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987529

C5-152 JOURNAL DE PHYSIQUE

to the simple with increasing As composition. The densities and mobilities for both electrons and holes have been extracted by analyzing the positive magnetoresistance and the non-linear Hall voltage at low fields, and the Shubnikov-de Ilaas oscillations at the moderate fieldsf4,5). The physical parameters thus obtained

summarized m Table I. Both electrons and holes, - 8 ~ l O ~ ~ c m - ~ and . v 3 ~ 1 0 ~ ~ c m - ' with GaSb layers, are found to decrease monotonically with increasing alloy compositions

and y when the GaSb is replaced by GaSb,-,As, and Gal-&Sb . Only electrons are present with a density of 3-5x 101lcm-a beyond the limit of x-0.2 and y 4 3 . The electron mobilities, however, can be kept h i g h than lWm2/V-sec within these limits, and they appear to be influenced mainly by the lattice misnatch between InAs and the alloys. In addition, alloy scattering

t o play a role for the rather abrupt reduction of hole mobilities in the alloyed quantum wells. The imbalance between electron and hole densities implies that extra charged states exist in the vicinity of the interface, which shift the Fenni level from its ideal position. The rather similar behavior of the two types of alloys suggests that the relative band edge positions are insensitive to the cation-anion nature of the substitutional elements in GaSb[4].

Now we discuss the puzzling behaviors of the semimetal-like quantum wells. The magneto-resistanm peaks are compared with those of the single electron

0.3), taking into account the difference in electron densities among the three different samples. Almost all the

can be identified to be mainly due t o electron Landau levels, as indicated by the numben and the arrows in Fig.2. Some of the peaks, for instance at

for

0.15

for y = 0, however, can not be explained simply by the electrons. Momover, the electron-dominated peaks, 27 and

11, an accompanied by the unusual negative transitions in the quantum Hall plateaus. All these strwtum have also been observed in InAs-GaSb,-As, quantum wells. In both

the structures become more distinct with decreasing temperatures, implying that their

is intrinsic t o the electron-hole system; canier densities will fluctuate siguificantly with the application of magnetic fields.

Eased on such consideration, the density of

and hence the magnetoconductances, are calculated with the following bdundary conditions: maintaining the Fermi level continuous at the the heterointena~a, and conmving the charge neutrality including the imbalance between both carriers[6,7].

comparison was also performed for the single carrier

(y = 0.3) to coniirm the consistency of our calculations. The results are shown in Fig.3 to&er with

experimental data; the origin of every peak is now clear. In the y =0.15 case, for example, two processes are involved in the 2T peak; the Fermi level fist crosses the lowest hole Landau level at the &st half of the peak and it

the fifth electron Landau level at the second hatf. Because of such sequence, the &g factor of hole

v,

is firstly reduced from 1 to 0, followed by the reduction of the electron filling factor

from

to 4. This results m the splitting in the quantum I-lall plateau with the dip located near the center (Fig.2)[6]. Around 6 . n . the reverse process takes place: the numbers of both carriers increase with magnetic fields, and the Fenni level crosses the hole Landau in the reverse direction. Consequently. the filling factor of holes gains,

1. Because of this, we have obscrved the additional peak at 6.5T. accompanied by the positivc transition in the Hall plateaus

from

to 3 (Fig.2)[8]. The same process is repeated at the

3 Hall plateau for the formation of the dip. Thereafter, holes are completely annihilated by the portion of electrons because the lowest hole Landau level rises above the Fermi level above -9T. The If peak is now purely due to the reduction of the electron filling factors, and, as seen in the experimental Hall voltage spectrum in Fig.2, the characteristic dip is no longer observcd in the

2 Hall plateau.

All the behavior is more pronounced in the y =

case (Fig.3). In this a, the antihidation of holcs occurs at - 2 n , because the number of holes here is three times higher than in the y

0.15.

In conclusion, we have examined a new approach to control canier densities

the type-11 quantum well

structures of Ids-GaSb. This is achievcd by changing the band schcmcs of the structures with the substitution of

the alloy composition, the natuxe of the conduction changes from semimetal-like to that of a single

For the semimetallic quantum wells, the electron and hole behave as individual parallel channels at the low magnetic fields, whereas they appear to be interconnected to each o t h i with increasing the magnetic field: the magneto-transport spectra reflect the change in carrier densities, leading to the annihilation of holes at high magnetic fields.

REFERENCES

1. L.L. Chang and L. Esaki, Surf. Sci. 98, (1980) 70.

2. E.E. Mendez, L.L. Chang, C.-A. Chang, L.F. Alexander, and L. Esaki, Surf. Sci. 142, (1984) 215; S. Washbum, R A . Webb, E.E. Mendez, L.L. Chang, and L. Esaki, Phys. Rev. B 31, (1985) 1198.

3. E.E. Mendez, L. Esaki, and L.L. Chang, Phys.

Lett. 55, (1985) 2216.

4. H. Munekata, L. Esaki, and L.L. Chang, J. Vac. Sci. Technol. B 5, (1987) 809.

5. H. Munekata, E.E. Mendez, Y. lye, and L. Esaki, Surf. Sci. 174, (1986) 449.

6. T. Smith, H. Munekata, F.F. Fang, L. Esaki, and L.L. Chang, the 7th Internl. Conf. on Elcctmnic Properties of Two Dimensional Systems, Sank Fe, July 1987.

7. Parameters used for the calculations arc

= 0.023m,, m, = 0.35% for carrier masses, and

= 12-15,

1 for g-factors, and T, =2.3meV and Tb=0.71meV for the Landau level broadenings, for electrons and holes, respectively. The

represents the mass of the free electron.

8.

4 and 3 mean

=

4-0 and

1, respectively; the idea of compensated filling factors are discussed in ref.3.

TABLE I. Densities

mobilities of electrons and

at 4.2K

the

quantum wells.

Fig.1 Schematic band diagrams for the .heterojundion of three diffe&nt InAs-GaSb b a d alloys; (a) In&-GaSb, (b) U s - Ch~Alo.,Sb, and

U s - Ga&b,Sb. The same trend holds for Ids-GaSb,-as, with incr+asing r

N (cm-7 P (an-7

(ma/V*scc)

(cma/V-sec) 8 . 4 ~ 10" 3 . 6 ~ 10" 1 . 6 ~ 10' 1 . 4 ~ 1W 6 . 6 ~ 10" 1 . 2 ~ 10" 1.6~10' 5 . 5 ~ 1B 5.3~10" - ^{1 . 6 ~ 10'}

3 . 0 ~ 10" - ^{6 . 5 ~ 10'}

7 . 2 ~ 1011 1 . 3 ~ 10" 1 . 9 ~ lW 4 . 5 ~ lo' 7 . 0 ~ 1 0 ~ ~ 1 . 0 ~ 1 0 ~ ~ 1.5~10' 4 . 5 ~ lo' 2x10" - ^{1 . 4 ~ lo)}

Sample InAs-GaSb LnAs- Ga,-&Sb InAs GaSb,-&

x

and y 0 0.15 0.3 0.5 0.07 0.12 0.25

Ada-

0.61

0.71

0.81

0.94

0.1

-0.45

-1.2

C5-154 JOURNAL DE PHYSIQUE

MAGNETIC FIELD (teslo)

Fig.2 Magneto-resistance (a) and Hall-resistance @)

=P=C'=

at 0.4K for the

G&b/InAs(20nm)/GaAlSb quantum wells with thne different A1 compositions.

MAGNETIC FIELD (Tesla)

Fig.3 Calculated magneto-nsistana spectra (solid

using the two-channel model with electron

and hole densities of 8 3 and 27x 101lcm-a for y = 0,

6.4 and 0 . 8 ~ l O ~ ~ c m - ~ for y = 0.15, and 5 3 ~ 1 0 ~ ~ c m - ~

(no holes) for y = 0.3, respectively. Experimental

data

also shown in broken curves.