Sensors and Actuators A 113 (2004) 365–369

Photocurrent spectroscopy of GaInNAs and GaInNAs(Sb) strainedquantum wells grown by molecular beam epitaxy

S. Ben Bouzida,∗, F. Bousbiha, R. Chtouroua, J.C. Harmandb, P. Voisinb

a Unité de Recherche de Physique des semiconducteurs de l’Institut Préparatoire aux Etudes Scientifiques et Techniques,BP 51, 2070 La Marsa, Tunisia

b Laboratoire de Photonique et de Nanostructures, CNRS, Route de Nozay, 91460 Marcoussis, France

Received 10 June 2003; received in revised form 23 January 2004; accepted 26 January 2004

Available online 21 April 2004

Abstract

We have investigated the interband transitions in strained GaInNAs/GaAs and GaInNAs(Sb)/GaAsSbN quantum wells (QWs) usingabsorption spectra. The experimental data are compared with a calculation in the envelope function formalism taking into account theeffects of strain and the bandgap lowering due to the strong coupling between nitrogen-localized states and the extended states of III–Vconduction band. The results are consistent with a type I band alignment and a conduction band offset ratio of about 80%. They alsoindicate an increased electron effective mass in III–V–N QWs in comparison with III–V materials. QW gap in the 1.5�m range is achievedon the GaAs substrate using GaInNAsSb/GaAsSbN single QW.© 2004 Elsevier B.V. All rights reserved.

PACS:71.23.An; 71.28.+d; 71.35.Cc

Keywords:GaInNAs; GaInNAsSb; Optical sensors; Semiconductors; Lasers

1. Introduction

The GaInNAs semiconductor alloy is being intensivelystudied due to its fundamental properties[1,2] and deviceapplications in high performance laser diodes emitting at1.3�m optical fiber window[3,4], optical sensor[5], andhigh efficiency multijunction solar cells[6]. It has beenfound that the incorporation of only 2% nitrogen in GaInAsdecreases the band gap energy by more than 200 meV[7].When the In mole fraction is approximately three timesthe N mole fraction, i.e.x ∼= 3y, Ga1−xInxNyAs1−y/GaAscan be grown closely lattice matched to GaAs. The roomtemperature pulsed operation of 1.3�m laser diodes usingGa0.9In0.1N0.03As0.97 lattice matched to GaAs has been ac-complished[3]. But, the photoluminescence (PL) intensityrapidly decreases while the linewidth increases with in-creasing nitrogen incorporation[8–11]. The crystal qualitycan be improved by thermal annealing, and the PL intensityin Ga1−xInxNyAs1−y layer can be significantly enhanced.However, thermal annealing results in a large PL peak shift to

∗ Corresponding author. Tel.:+216-71929841; fax:+216-71560723.E-mail address:sihembenbouzid@yahoo.fr (S. Ben Bouzid).

a shorter wavelength region[12]. In order to achieve 1.3�mwavelength and maintain reasonably high quality crystal,one effective method is to increase the In mole fraction anddecrease the N mole fraction simultaneously. Increasing theIn mole fraction, i.e.x > 3y, results in compressive strainin the GaInNAs layer. Using this method, 1.3�m roomtemperature cw operation of Ga0.7In0.3N0.01As0.99 com-pressive strained QW has been successfully achieved[13].Compared with conventional GaInPAs/InP laser diodeswhich have a poor characteristic temperature (T0) of 50–70[14], GaInNAs/GaAs laser diodes have better temperaturecharacteristics. This is due mainly to the larger bandgapdifference between GaInNAs and GaAs. While GaInNAscan have a small band gap energy, wavelengths are actu-ally limited by the N solubility limit and the high In strainlimit. Recently, GaInNAsSb alloy was proposed, as a newsystem for 1.3–1.6�m long wavelength laser[15] on GaAssubstrate. In order to understand the band structure, in-terband transitions in GaInNAs and GaInNAsSb QWs areinvestigated using photovoltage (PV) measurements. Theexperimental data are analyzed using the envelope functionformalism and taking into account the effects of strain andthe strong coupling between nitrogen-localized states andthe extended states of III–V conduction band.

0924-4247/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.sna.2004.01.056

366 S. Ben Bouzid et al. / Sensors and Actuators A 113 (2004) 365–369

2. Experimental details

The following structure was grown by molecular beamepitaxy on an n-type GaAs (1 0 0) substrate using a radiofrequency (rf) N radical beam source. The active regionconsists of 7 nm GaIn0.37N0.013As or GaIn0.4N0.01AsSb0.015quantum wells sandwiched between 100 nm undoped GaAswaveguide layers. The GaInNAsSb single QW is surroundedby GaN0.01AsSb0.015 barriers. A 1.5�m Si-doped (7×1017)n-type Al0.8Ga0.2As cladding layers was grown betweenthe n+-GaAs buffer layer (0.2�m) and the active layer. A1.5�m Be-doped (5× 1017) p-type Al0.8Ga0.2As claddinglayers followed the active layer. Conventional InZn metal-lization was used for the p-type contact. The growth temper-ature for the QWs, the GaAs waveguide layer, and AlGaAscladding layer were 400, 510, 550◦C, respectively. To de-termine the N and In mole fraction, both X-ray diffractionand pre-calibrated photoluminescence (PL) investigations ofInGaAs structures were performed. In and N compositionswithin the InGaNAs layer were estimated as 0.37 and 0.013,respectively. A schematic diagram of the GaInNAs (GaIn-NAsSb) QW structure is shown inFig. 1.

The PV spectra were performed using a halogen lampdispersed by a 0.32-m monochromator. The choppedmonochromatic light was incident on the top of the sam-ple, and the capacitively coupled photoresponse signal wasobtained by measuring the open circuit voltage (Voc) usingthe lock-in amplifier.

3. Results and discussion

Studies of the optical properties of GaInNAs/GaAs andGaInNAs(Sb)/GaAsSbN QWs have mostly concentrated onabsorption measurements to explore the optical transitionsbetween the quantized electron (e) and hole states. Absorp-tion coefficientα(λ) of these structures are determined us-ing PV spectra as discussed in ref.[16]. When the incidentlight powerW � 1/α, theVoc(λ) signal of the sample canbe described as[16]:

Voc(λ) = ηqI0W

chνα(λ) (1)

InZn metal

p-AlGaAs Clad (1.5 µm)

n-AlGaAs Clad (1.5 µm) GaAs Waveguide (100 nm)

Active Layer

n-GaAs Buffer Layer (0.2 µm)

n-GaAs Substrate

Fig. 1. Schematic diagram of the GaInNAs (GaInNAsSb) QW structure.

0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30

0.0

0.5

1.0

1.5

E1-L1

E1-H3E1-H1

E2-H2

T=300K T=2K

PV

(a

. u

.)

Energy (eV)

0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.300.0

0.5

1.0

1.5

2.0

2.5

E1-L1E2-H2

E1-H1

T=300K T=2K

PV

(a

. u

.)

Energy (eV)

(a)

(b)

Fig. 2. Room- and low-temperature PV spectra of GaIn0.37N0.013As/GaAssingle (a) and three quantum wells (b).

where η, I0, hν, and c represent the collection efficiencyof photogenerated carriers, length of surface depletion re-gion, photon energy, and the equivalent capacitance, respec-tively. Under such condition,Voc is proportional toα(λ),and the line shape of PV spectra will be the same as ab-sorption. It is noted, however, at low temperature the PVsignal decreases due to the low efficiency of the photo-generated electrons and holes collection due to high en-ergy barriers between the active region and the claddinglayer.

Room and low temperature PV spectra of GaIn0.37N0.013As/GaAs single and three quantum wells are shown,respectively, in Fig. 2a and b. Well-defined absorp-tion steps are observed even at room temperature inPV spectra for single and triple GaIn0.37N0.013As/GaAsQWs. Fig. 3 shows room temperature PV spectra ofGaIn0.40N0.01As(Sb0.015)/GaAsSb0.015N0.01 SQW. As seenhere, the incorporation of a small amount of Sb is sufficientto shift the fundamental gap down to 850 meV at 300 K.Arrows in Figs. 2a, b and 3show calculated transitionsusing the nominal quantum well thickness, as discussedbelow. The confined energies of electrons, heavy and lightholes are calculated using envelope function approximation.The unstrained band gap energyEust

g of III(Ga, In)–V(As,Sb)–N layer is determined using the band anticrossing

S. Ben Bouzid et al. / Sensors and Actuators A 113 (2004) 365–369 367

0.8 0.9 1.0 1.1 1.2

Energy (eV)

1.3

0.0

0.5

1.0

1.5

2.0

QW)(1(b)-H 1E

b)(1(b)-H 1ET=300K

1-HE1-L 1E1

a.u

)P

V (

Fig. 3. PV spectra of GaIn0.40N0.01As(Sb0.015)/GaAsSb0.015N0.01 SQW atroom temperature.

model (BAC)[1]:

Eustg (III–V–N )

= 1

2

{EN + EIII –V −

√[EN − EIII –V]2 + 4V 2

N–III –V

}(2)

whereEN andEIII –V are the energies of the nitrogen-localizedstate and of the matrix III–V band edge, respectively, andVN–III –V is the matrix element describing the interactionbetween those two types of states. The strained band gapenergy Est

e−hh(lh)(III–V–N ) between the electron and theheavy (light) hole bands is determined taking into accountthe hydrostatic and shear components of the strain, given by:

Este−hh(III–V–N ) = Eust

g (III–V–N ) + Ehyd + Esh (3)

Este−lh(III–V–N ) = Est

e−hh(III–V–N ) − 1.5Esh

+ 0.5∆so

⌊1 −

√1 + 2Esh/∆so + 9E2

sh/∆2so

⌋

Ehyd =⌊

2(p + �p)(C11 − C12)

C11

⌋ε (4)

Esh =⌊−q(C11 + 2C12)

C11

⌋ε

where p and q are respectively the hydrostatic and sheardeformation potentials, andCij the elastic constants in

Table 1Parameters of GaAs and InAs

GaAsa InAsa

Lattice constanta0 (Å) 5.653 6.058Elastic constantC11 (GPa) 11.879 8.329Elastic constantC12 (GPa) 5.376 4.526Deformation potentialp (eV) −6.7 −6.08Deformation potentialq (eV) −1.7 −1.8Spin–orbit splitting∆so (meV) 340 380

a Reference[20].

Table 2Bowing coefficient of ternary alloys used in the calculation

Alloy Bowing coefficienta

Ga(As, Sb) 1.200In(As, Sb) 0.580(Ga, ln)As 0.380(Ga, ln)Sb 0.420

a Reference[21].

(In, Ga)As system;∆so is the spin–orbit splitting whichis independent of nitrogen content[17]; �p is the sheardeformation potential term correction due to N and Sb inIII–V materials; ε is relative strain in the plane direction.The different calculation steps of the strained III–V–Nbandgap energies are summarized in the scheme givenbelow:

{(Ga, In)As + NBAC−→ (GaInNAs)ust strain effect−−−−−→ (GaInNAs)st

{Ga(As, Sb)+NBAC−→ (GaAsSbN)ust strain effect−−−−−→ (GaAsSbN)st

Tra

nsiti

on E

nerg

y (e

V)

∆me

∆ p=15 % ∆ p=11 % ∆ p=6 % ∆ p=0 %

Exp

2E2-H

1E1-L

3E1-H

E1-H1

1.25

1.20

1.15

1.10

1.05

1.00

0.95

0.080.060.04

)(m0

0.02.0000.90

∆ p=30 % ∆ p= 0 %

Exp

E2-H

2

E1-L

1

H3

E1-

E1-H

1

Tra

nsiti

on E

nerg

y (e

V) 1.1

1.0

0.9

0.00 0.02 0.04

∆me

0.06

)0.08 0.10

(m0

(a)

(b)

Fig. 4. Room-temperature transitions energies of GaIn0.37N0.013As/GaAsQWs (a) and GaIn0.40N0.01As(Sb0.015)/GaAsSb0.015N0.01 SWQ (b) asfunction of the electron effective mass term correction with the theoreticalfit (solid and dashed lines) for different�p shear deformation potentialterm correction.

368 S. Ben Bouzid et al. / Sensors and Actuators A 113 (2004) 365–369

{Ga(As, Sb)

In(As, Sb)⇒ (GaInAsSb) + N

BAC−→ (GaInNAsSb)ust

strain effect−−−−−→ (GaInNAsSb)st

and the pertinent parameters used in the calculation are gath-ered inTables 1 and 2. The electron effective mass in theIII–V–N layer is taken as:

me(III–V–N ) = me(III–V ) + �me (5)

where me (III–V) is the electron effective mass in III–Vmaterial and�me is the electron effective mass term cor-rection resulting from the flattening of the conduction bandunder nitrogen effect. The strained conduction band offsetused in our calculation is about 80% of the strained heavyhole–electron bandgap difference; this value is the same asfor GaInNAs/GaAs QWs with comparable indium and ni-trogen contents[18].

Fig. 4a shows GaIn0.37N0.013As/GaAs QWs calculatedtransitions energies plotted as a function of the electroneffective mass correction for different shear term correction�p. Observed transitions energies are indicated as darksquares. It is seen inFig. 4a that the E2–H2 transition issensitive to the effective mass variation. A reasonable agree-ment is found for the E1–H1, E1–H3, E1–L1 and E2–H2data using�p/p = 0.11 and�me = 0.035m0. However,the E2–H2 transition energy is also very sensitive to the

Fig. 5. Room-temperature band-edge profiles for GaIn0.37N0.013As/GaAs(a) and GaIn0.40N0.01As(Sb0.015)/GaAsSb0.015N0.01 (b) quantum wells.

QW thickness, which is not measured independently inthis study. Note also that the qualitative assessment of theupper lying transitions is non-trivial. A full calculation ofthe absorption spectra, including the transition oscillatorstrength, would help elucidating the remaining ambiguities.Fig. 4b shows that the E1–H1 and E1–L1 measured transi-tions of GaIn0.40N0.01As(Sb0.015)/GaAsSb0.015N0.01 SQWare in agreement with the theoretical fit for�p = 0.3p

and �me = 0.035m0. We note that the incorporation offew percentage of Sb in GaInAsN material reduces sig-nificantly the strain and the presence of N increases theelectron effective mass as theoretically[19] predictedand experimentally observed by Hetterich et al.[18] ina GaInNAs alloy with 1.5% N. Finally, taking into ac-count of all fit parameters, we have plotted inFig. 5the band-edge profiles of GaIn0.37N0.013As/GaAs andGaIn0.40N0.01As(Sb0.015)/GaAsSb0.015N0.01 QWs showingthe type I band alignment. We note that the incorporationof Sb in GaInNAsSb/GaAsNSb have reduced the funda-mental gap energy and the electron potential depth from418 to 340 meV by comparison with GaInNAs/GaAs QWs.The reduction of the electron potential depth in GaIn-NAsSb/GaAsNSb lead us to assume that the two transitions1.125 and 1.250 eV in PV spectra (Fig. 3) can be attributedto free-to-bound E1(b)–H1(QW) transition and E1(b)–H1(b)barrier transition, respectively.

4. Conclusion

In summary, PV measurements were used to determine theinterband transition energies in GaInNAs/GaAs and GaIn-NAs(Sb)/GaAsSbN QWs grown by molecular beam epi-taxy. The strain effects and the strong coupling betweennitrogen-localized states and the extended states of III–Vconduction band are taken into account to explain the ex-perimental data. The theoretical fit indicate an incrementof the electron effective mass and a reduction of the shearstrain in III–V–N material. The incorporation of few per-centage of Sb in GaInNAs material allows to the In contentup to 40% and decreases the shear strain. QW gap in the1.5�m range is achieved on the GaAs substrate using GaIn-NAsSb/GaAsSbN single QW.

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Biographies

S. Ben Bouzidreceived the B.S. degree in physics in 1999, and the M.S.degree in quantum physics in 2001, both from the Science Universityof Tunis, Tunisia. She is currently working toward the Ph.D. degree inphysics, where she is studying the dilute nitride (Ga, In) (N, As, Sb)based system for applications in long-wavelength lasers on GaAs.

F. Bousbih received the B.S. degree in physics in 1998, and the M.S.degree in quantum physics in 2000, both from the Science Universityof Tunis, Tunisia. She is currently working toward the Ph.D. degreein physics, where she is studying the dilute nitride GaAs system forapplications in long-wavelength optoelectronic devices.

R. Chtouroureceived the B.S. degree in physics in 1983, and the M.S.degree in solid physics in 1985, the Ph.D. degree in quantum physics in1996 and the academic authorization in 2003 all from the Science Uni-versity of Tunis, Tunisia. His research interests are III–V heterostructureson GaAs substrate and III–V heavily doped nitrogen for long-wavelengthoptoelectronic applications. He is currently a master of conference atPhotovoltaic and Semiconductor Laboratory of National Institution ofResearch and Technology.

J.C. Harmandwas born in Paris in 1959. He obtained his Ph.D. in physicsat the University of Paris 7 in 1988 for his work on GaAlAs/GaAs HBTs.From 1988 to 1990, he was at the Optoelectronic Research Laboratoryof Matsushita (Osaka, Japan) where he was involved in studies on meta-morphic AlGaInAs/GaAs HEMTs. From 1990 to 1999, he was engagedin III–V growth for micro and opto-electronics at CNET/France Telecom.Since 2000, he conducts epitaxial growth research at LPN/CNRS. He isauthor and coauthor of more than 150 papers and communications in theIII–V materials and device fields.

P. VoisinDirecteur de Recherche at CNRS. He presently leads a group atthe Laboratory for Photonic and Nanostructures. His interest has coveredmany aspects of semiconductor heterostructure physics, with a focus onelectro-optical and magneto-optical properties.