Liquidphase epitaxial growth of GaInAsSb with application toGaInAsSb/GaSb heterostructure diodesMengChyi Wu and ChiChing Chen Citation: J. Appl. Phys. 71, 6116 (1992); doi: 10.1063/1.350419 View online: http://dx.doi.org/10.1063/1.350419 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v71/i12 Published by the American Institute of Physics. Related ArticlesEffect of hafnium addition on Zn-Sn-O thin film transistors fabricated by solution process Appl. Phys. Lett. 100, 022109 (2012) Four degree of freedom liquid dispenser for direct write capillary self-assembly with sub-nanoliter precision Rev. Sci. Instrum. 83, 015104 (2012) Ultraviolet assisted processing: A unique approach to mitigate oxygen vacancies and attain low loss highlytunable Ba0.60Sr0.40TiO3 thin films J. Appl. Phys. 110, 124105 (2011) Inkjet printing of single-walled carbon nanotube thin-film transistors patterned by surface modification Appl. Phys. Lett. 99, 183106 (2011) Organosilane deposition for microfluidic applications Biomicrofluidics 5, 036501 (2011) Additional information on J. Appl. Phys.Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors

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Liquid-phase epitaxial growth of GalnAsSb with application to GalnAsSb/GaSb heterostructure diodes

Meng-Chyi Wu and Chi-Ching Chen Research Institute of Electrical Engineering, National Tsing Htla University, Hsinchu, Taiwan 30043, Republic of China

(Received 27 November 1991; accepted for publication 10 March 1992)

High quality Gaod”o. &so. Gbo.83 layers lattice matched to GaSb substrates were grown by liquid-phase epitaxy using a supercooling technique. By selection of the optimum growth condition, we can obtain the undoped layer with a low hole concentration of 1.2 x 10’” cm-’ and a narrow full width at half maximum of 12 R photoluminescence spectrum of 11.6 meV. The temperature dependence of near band gap energy in G~,saIno.,sAso,17Sb0.83 layers, determined from the photoluminescence peak energy, varies as 0.62-[5.2X 10-4T2/( T+ 163)] eV. In order to obtain the low electron concentration layer, the Te-doped polycrystalline GaSb (n =4x 10” cm --‘) is used to replace some of the undoped GaSb starting material in the growth solution for the purpose of compensation. The lowest hole concentration of 4-7 x 10’” cm-” can be achieved when the GaSb starting material in the growth solution consists of 10% Te-doped

L polycrystalline. With increasing percentage, the layer conduction changes to n type, and it reaches an electron concentration of 2x 1017 crnm3 by using only the Te-doped GaSb polycrystalline in the growth solution. On the other hand, the peak wavelength of 12 K photoluminescence spectrum decreases with increasing elec.tron concentration because of the Burstein-Moss effect. Finally, an n-GaInAsSbi’p-GaSb heterostructure diode was fabricated, which exhibits a forward-bias turn-on voltage of 1.8 V and an ideality factor of 1.86.

I. INTRODUCTION

It has been predicted from theoretical considerations that losses as much as two orders of magnitude lower than those of silica fibers may be achieved for the heavy metal fluoride fibers in the 2-4 pm wavelength region.’ One 111-V alloy system that offers the possibility of achieving the de- sired band gap and lattice matching to a binary substrate is Ga,-,In,As,Sbt_, grown on either InAs or GaSb sub- strates.

The band gaps of Gal ~&r,As,Sbi --y quaternary alloys lattice matched to GaSb (v/x-0.9) are direct and corre- spond to wavelengths between 1.7 and 4.3 pm. Unfortu- nately, a wide solid phase miscibility gap limits the work- ing wavelength domain of the GaInAsSb alloy to less than 2.4 pm. 2*3 There has been a considerable effort to study the phase diagram and growth of these materials by liquid- phase epitaxy (LPE) .2*4,5 Kobayashi et aL6 reported the L.PE growth of GaInAsSb on (100) GaSb at 527 “C for xgO.092. Kano et a1.7 have studied the GaInAsSb growth on ( 111 )B GaSb at 595 “C for x<O. 18. Nakajima et al.’ reported the growth of GaInAsSb on GaSb for O<x<O.4 and on InAs for 0,7<x<l.O. Recently Tournie et aL9 re- ported that the cutoff wavelength of GaSb lattice-matched GaInAsSb LPE layers can be changed from 2.38 to 2.51 ym, by using ( 11 l)B orientation GaSb substrates instead of the (100) orientation, and high melt supersaturation. Also, the molecular beam epitaxy (MBE) of GaInAsSb on GaSb with a band gap of 0.59 eV (2.1 pm in wavelength) was reported by Tsang et al. lo Cherng et al.” reported the metalorganic vapor phase epitaxy (MOVPE) of metasta- ble GaInAsSb alloys throughout the range of solid immis- cibility. A number of studies have reported the radiation

emission of GaInAsSb heterostructures on GaSb sub- strates. These results include optical, pumping,‘” electron beam pumping,‘“Ti4 and injection lasers.i5-‘s It is worth mentioning that unintentionally doped GaInAsSb epitaxial layers always give a p-type conduction with a high back- ground concentration in the l-3 x 10” crnM3 range.2’1” It is very difficult to obtain good performance of GaInAsSb photodiodes with the high residual acceptor concentration. Srivastava et al. XJ have fabricated room-temperature GaInAsSb/GaSb photodiodes for use at wavelongths to 2.3 pm by using Te compensation of the quaternary layer. Bowers et al. have obtained good performance of GaInAsSb/GaSb p-i-n photodetectors for wavelengths to 2.3 pm with introducing a nearly compensated it-type Sn- doped GaInAsSb layer.‘” Law et al. have also reported the AlGaAsSb/AlGaSb avalanche photodiode operating from 1 to 1.4 pm by using Te compensation in the AlGaAsSb layer.‘l However, there are no detailed reports on the char- acterization of GaInAsSb layers with low net carrier con- centration.

In this paper, we report the growth and characteriza- tion of high quality 2.3 (-‘m Gao.RzIn,IsAs,,17Sb0.83 layers on (lOO)-oriented GaSb substrates by LPE, and the fabri- cation and performance of GaInAsSb/GaSb heterostruc- ture diodes.

II. GROWTH AND CHARACTERIZATION OF UNDOPED AND Te-DOPED GalnAsSb LAYERS

Ga,.Jn&$bl-, were grown by LPE in a sliding boat system under a flowing hydrogen ambient. The melts used to grow GaInAsSb quaternary layers were composed of 6-9’s In and Sb, undoped polycrystalline InAs and

6116 J. Appi, Phys. 71 (12), 15 June 1992 0021-8979/92/126116-05$04.00 @ 1992 American Institute of Physics 6116

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G&b. After having been cleaned and et.ched, appropriate amounts of Sb, InAs, and GaSb were added to the 3 g In metal to form the Gao.14Y71n0,595Asi),~13SbC).255 growth so- lution. The melt was then prebaked at 700 “C for 10 h or more to reduce the oxides that tend to form in the melt and to obtain a low carrier concent.ration in the epitaxial layer. The substrates used were undoped or Te-doped (loO)- oriented G&b with a carrier concentration OF 3-6X 1017 CID i 3 and an etch pit density of less than 5 X 10” cm--‘. After loading the wafer, evacuating, and purging with pu- rified hydrogen, the melt was heated to 560 “C for 1 h to completely redissolve the growth solution. Prior to growth, the substrate was etched itl s&r with an undersaturated G&b solution for 3-5 s to remove the thin residual oxide layer on the GaSb surface. The epitaxial layer was imme- diately grown near 527 “C by means of the supercooling technique with a 6 “C supersaturation, at the cooling rate of 0.3 “C/min. The thickness of GaInAsSb epitaxial layers grown during a desired growth period of 5 min was typi- cally 6 /km.

The undoped grown layers were typically p type. In order to achieve the low electron concentration, the Te had to be added to the growth solution in very small quantities ( < 1 jig) because of the high Te segregation coefficient.22 To accomplish this, the polycrystalline Te-doped GaSb with an electron concentration of 7.4X 10’7 cm- 3 (from MCP Co.) was used to replace some of the nominally un- doped GaSb (residual p-type background) starting mate- rial.

Single-crystal x-ray diffraction, Fourier transform in- frared (FI’IR) spectroscopy, photoluminescence (PL), and electrochemical capacitance-voltage ( C-I’) measure- ments were carried out to characterize the GaInAsSb epi- taxial layers. Details of growth conditions and character- ization techniques were given elsewhere.““-‘” For all the undoped and Te-doped GaInAsSb samples, the surface morphology is very shiny and flat,. The interface between epitaxial layer and Gash substrate is also flat and free from inclusions. Lattice mismatch between the epitaxial layer and substrate normal to the wafer surface is controlled to within 0 to +r3.03%% which can obtain the best layer qual- ity.“” The solid composition of Gal -,In,As,Sbt --y epitax- ial layers is x=0.18 and ~~0.17, measured by a wavelength-dispersive x-ray spectrometer ( WDS) and cal- ibrated through ZAF (atomic number, absorption, and flu- orescence) correction. This composition corresponds to a predicted wavelength of -2.3 /l.rn for this material.’ The room-temperature wavelength for the GaInAsSb epitaxial layer estimated from FTIR measurements is 2.27 pm, which corresponds to a band gsp of 0.546 eV. This agrees closely with the data derived by DeWinter et aL2 Figure 1 shows the 12 K PL spectrum of the undoped GaInAsSb layer with a low background hole c.oncentration of 1.2 >< l(p cnl-3, which is used as a reference sample. It shows only one emission peak at 2.005 pm associated with free electron-to-free hole recombination and no other impurity peak, such as conduction band-to-acceptor level transi- tjon,20,27 is observed. This fact indicates that the acceptor defect which is generally present in antimonide compounds

6117 J. Appl. Phys., Vol. 71, No. 12, 15 June 1992

1.9 2.0 2.1 2

WAVELENGTH @ml

FIG. I. 12 K photoluminescence spectrum of the undoped G~,B?In,,,sAso,,7Sb0.83 layer grown on GaSb substrate with a hole con- centration of 1.2X lOi cm-‘.

has disappeared and/or is compensated. The full width at half maximum (FWHM) of this 12 K PL spectrum is 11.6 meV, which is better than or comparable to the best results previously reported on similar composition layers grown by LPE (9 meV at 2 K with x=0.26 and y=O.23, 20 meV at 2 K with x=0.23 andy=0.20),’ MBE (13 meV at 2 K with x=0.24 and y=O.2O),‘s and mctalorganic vapor phase epitaxy (MOVPE) (38.8 meV at 6 K with x=0.32 and y=O.30, the alloy being inside the immiscibility re- gion) ‘1 techniques.

Figure 2 shows the variation of the photon energies of the near band gap peak as a function of temperature for the undoped Ga,,s-&-,, tsAso, t7Sb0,s3 epitaxial layer. The tem- perature dependence of the band gap in this figure can be expressed by the Varshni equation:29

E,(T) =E,(O) -aZ’2/(~+B>,

where E,(O) is the energy gap at 0 K, and o and p are material constants. The calculated Es(O), iy, and /3 by the least-square method are 0,620 eV, 5.2X lo-” eV/K, and 163 K, respectively. Temperature dependence of the FWHM of the near band gap peak is also shown in Fig. 2. The somewhat larger FWHM than the theoretical value of 1.85 kT3’ may be due to the existence of another radiative transition process, such as residual shallow donor-to- valence band recombination, very near to the band-to-band transition peak.

In order to reduce the background carrier concentra- tion, we used Te-doped GaSb as part of the source material for the purpose of compensation. The Te-doped GaSb re- places anywhere from 0% (all polycrystalline GaSb source material) to 100% (all Te-doped GaSb) by weight of the GaSb source. Figure 3 shows the room-temperature carrier concentration of a Te-doped G~.s21n,,18AS0,17Sb0.83 layer grown on a GaSb substrate, measured by the electrochem-

M.-C. Wu and C.-C. Chen 6117

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_ Te-Doped Go ,Jn 0.8 0.lP~O.l ,Sbo.e,

II--I - I 0 100 200

TEMPERATURE ( K 1

IO

!O TG E

E

E Ok

_I a

0

FIG. 2. Variation of the photon energies and full width at half maximum of the near-band gap peak as a function of temperature for the undoped GaInAsSb layer.

ical C-V method as a function of the weight percent of Te-doped polycrystalline GaSb in the undoped polycrystal- line GaSb in the growth solution. Layers prepared without compensation were p type with net hole concentrations in the 1-3~ 10’7 cmw3 range. However, we can obtain high quality GaInAsSb epitaxial layers with a hole concentra- tion around 1 X 10” cme3 from the optimum growth con- dition.23 The hole concentration falls off to 4-7x 10” cme3 as the weight percent of Te-doped GaSb polycrystal- line is increased to 10%. By increasing the percentage, the conduction type will gradually change from p to iz type. When the percentage is increased further, the electron con- centrrntion increases linearly from 2 X 10’” crnm3 at the per- centage of 40% to 2 X 10” cmw3 as the undoped GaSb polycrystalline was completely replaced by Te-doped GaSb in the growth solution.

The 12 K PL spectra in the Te-doped Gao.s21110,18As0,17Sb0.83 layers also show only one emission band due to the recombination of free electrons and free holes, as seen in Fig. 1 for the undoped layers. The FWHM and peak wavelength of the 12 K PL. peak in Te-doped GaInAsSb layers as a function of the percentage of Te- doped polycrystalline GaSb in the growth solution are shown in Fig. 4. The FWHM curve has a value of 11.6 meV for the undoped layer and decreases to a minimum of

WE:FI-;T PERCENT OF Te-DOPED GaSb ! I\! Lil \ lOOPED POLYCRYSTALL / NE GaSb

FIG. 3. Room-temperature carrier concentration of Te-doped GaInAsSb layer grown on GaSb substrate measured by the electrochemical C-Y method, as a function of the weight percentage of Te-doped GaSb in undoped polycrystalline GaSb in the growth solution.

11 .l meV by reducing the net hole concentration. After passing through this minimum point with an increase in the percentage, the FWHM curve rises again and reaches a maximum of 20.2 meV for the case in which only Te-doped polyc.rystalline GaSb is used as the starting material in the growth solution. When the electron concentration in- creases from 2 to ‘20~ lOi cm-’ or the percentage is in- creased beyond 40%, the observed peak shifts toward the high-energy side from 2.005 to 1.967 pm. The shift, known as the Burstein-Moss shift,3’ is due to the filling of the conduction band and has been observed in other heavily doped n-type materials such as GaAs,“‘.“” InP ” InGaAsP 35 and GaSb.36$37 This shift is more pronounced in n-type ;han in p-type material because of the lower den- sity of states at the bottom of the conduction band. The Burstein-Moss effect occurs at the moderate electron con- centrations, perhaps because of the much lower density of states of conduction band for the low band gap material (E,=O.546 eV).

Ill. FABRICATION AND PERFORMANCE OF GalnAsSb/GaSb DIODES

The reported p-u heterostructure diode consists of an n-type GaInAsSb layer grown by LPE on a ( lOO)-oriented p-type GaSb substrate (p= 14X 1017 cmm3). The GaInAsSb epitaxial layer is 6 pm thick and has an electron concentration of 4X lOi cmmd3, which was accomplished

6118 J. Appl. Phys., Vol. 71, No. 12, 15 June 1992 M.-C. Wu and C.-C. Ghen 6i18

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4 b-l ‘-,-

‘\’

2 3.

P 2 t; iz

ii .oo

0”

E P Y 2 %

.95 z L

-2

- I

WEIGHT PERCENT OF Te-DOPED G&b

IN UNDOPED POLYCRYSTALLINE G&b

FIG. 4. The full width at half maximum and peak wavelength of 12 K PL peak in Te-doped CMnAsSb layers a5 a function of the weight percent of ‘l’r-doped G&b in undoped polycrpstalline GsSb in the growth s&&n.

by using the percentage of 50% Te-doped polycrystalline GsSb in the undoped G&b starting material. After the growth process, the substrate side was thinned to about 3w) pm in order to reduce the bulk resistance. The wafer was then etched in a diluted HCI soIution for 15 s to re- move surface oxide. The IZ and p contacts were made to the epitaxial layer and substrate by evaporating Au/N/Au/ Gemi and Au,Kr, respectively, After deposition, the wa- fer was alloyed at 301) “C for 3 min in a nitrogen ambient to obtain good ohmic contacts. Mesa geomet.ry diodes 135 Elm in diameter were defined using standard photolitho- graphic techniques and formed using a bromine/methanol etching solution. The wafer was then sawed into the die dimension of 500 fern :K 800 pm. The schematic cross sec- tion of the GaInAsSbiGaSb heterostructure diode is shown in Fig. 5.

The current-voltage (1-V) characteristic of the hetero- structure diode at room temperature is shown in Fig. 6. It exhibits a forward-bias turn-on voltage of 0. IS V with an ideality factor of 1.86. In the reverse direction, the soft breakdown phenomenon is observed and the breakdown voltage occurs as low as -1.8 V. We attribute this low breakdown voltage to the relatively small band gap of the GaInAsSb layer.

, , ~:::“,:~~osb

i Au/Cr CONTACT

FIG. 5. The schematic cross section of the GaInAsSb/GaSb hrterostruc- ture diode.

IV. CONCLUSIONS

High quality GaInAsSb epitaxial layers were grown on ( 100) GaSb substrates by the LPE technique. The epitax- ial layers were characterized by means of x-ray diffraction, Fourier transform infrared spectroscopy, wavdength- dispersive x-ray spectrometer, photoluminescence, and electrochemical C-Y measurements. The solid composition of the nearly lattice-matched quaternary layer is Gaa,,Ina18As0,17Sb0.Y3, which corresponds to a wavelength of 2.3 pm. Unintentionally doped GdIriAsSb layers always give p-type conduction with a carrier concentration above 1 X 10” cm ‘. By using the optimum growth condition, we can obtain a high-purity uncompensated epitaxial layer with a hole concentration of 1.2~ 10lh cm...‘” and a PL FWHM of 11.6 meV, which is better than or comparable to the results reported previously. The temperature depen- dence of the near-band gap peak in GaInAsSb layer varies as 0.62-[5.2 x lo-“T’/( T+ 163)] eV. In order to obtain the lightly n-type doped layer, Te-doped polycrystalline GaSb is used to replace some of the undoped GaSb starting material in the growth solution for the purpose of compen-

FORWARD: 0.2V/DIV,2.OmA/DIV

REVERSE: l.OV/DIV ,2.0mA/DlV

FIG. 6. The current-voltage charxteristic of the GalnAaSb/GaSb het- erostructure diode at room temperature.

6119 J. Appl. Phys., Vol. 71, No. 12, 15 June 1992 M.-C. Wu and C.-C. Chen 6119

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sation. The epitaxial layer still exhibits p-type conduction when the weight percentage of Te-doped to undoped GaSb is less than 20-30s. However, it changes to n type as the percentage is beyond 40%. The 12 K FWHM of the PL peak of Te-doped GaInAsSb layer increases with increas- ing electron concentration. On the other hand, the 12 K PL peak wavelength decreases from 2.005 to 1.967 pm as the electron concentration increases from 2 to 20x lOI cm -3, and this can be attributed to the Burstein-Moss effect. A Te-doped GaInAsSb epitaxial layer 6 pm thick and n=4~ 1Or6 cme3 was then grown on a p-type GaSb substrate to form a heterostructure. The n-GaInAsSb/p- GaSb diode exhibits a forward-bias turn-on voltage of 0.18 V and an ideality factor of 1.86.

ACKNOWLEDGMENTS

The authors wish to express their thanks to Dr. Y. K. Su and Dr. F. Y. Juang for their technical assistance. The work was supported by National Science Council under Contract Nos. NSCSO-0417-E007- 12 and CS80-02 10-D- 007-25.

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6120 J. Appl. Phys., Vol. 71, No. 12, 15 June 1992 M.-C. Wu and C.-C, Chen 6120

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