Technical Physics Letters, Vol. 30, No. 7, 2004, pp. 529–531. Translated from Pis’ma v Zhurnal TekhnicheskoÏ Fiziki, Vol. 30, No. 13, 2004, pp. 1–6. Original Russian Text Copyright © 2004 by Parkhomenko, Astakhova, Grebenshchikova, Ivanov, Kunitsyna, Yakovlev. Light-Emitting Diodes Based on Ga1 – xInxAsySb1 – y Solid Solutions Grown from Lead-Containing Melts Ya. A. Parkhomenko, A. P. Astakhova, E. A. Grebenshchikova, É. V. Ivanov, E. V. Kunitsyna, and Yu. P. Yakovlev Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia e-mail: www.ioffe.ru Received February 5, 2004 Abstract—Light-emitting diodes (LEDs) with the maximum emission at λ = 2.3 and 2.44 µm are obtained and characterized. The active region of LEDs is based on Ga1 – xInxAsySb1 – y solid solutions (x = 0.21 and 0.25, respectively) grown by liquid phase epitaxy from lead-containing melts. The room-temperature external quan- tum yield of the 2.3 and 2.44 µm LEDs is 1.6 and 0.11%, respectively. © 2004 MAIK “Nauka/Interperiodica”. Introduction. In recent years, much effort has been Methods of growth and investigation of LED devoted to the development and investigation of semi- structures. The LED heterostructures were grown by conductor optoelectronic devices emitting in the mid- liquid phase epitaxy (LPE) on n- and p-type GaSb(100) dle IR range (2–5 µm). This wavelength interval is of substrates. The wide-bandgap emitters were obtained interest for environmental monitoring and in some using a 2.5-µm-thick layer of GaSb. All layers in the medical applications. LED heterostructure were matched with respect to the lattice period with GaSb substrate (∆a/a < 1.0 × 10–3). The most promising materials for both sources and µ Equilibrium values of the molar fractions of solid solu- detectors of radiation in the 1.8–3.0 m wavelength tion components in the liquid and solid phases for the range are multicomponent solid solutions of the Pb–InAs–InSb–GaAs–GaSb system for selected Ga1 − xInxAsySb1 – y type based on gallium antimonide growth temperature (560°C) and supercooling (∆T = (GaSb). In this solid solution system, it is possible to 3 K) were calculated as described in [5, 6]. vary composition at a constant crystal lattice constant, thus controlling the bandgap width and, hence, the LEDs based on the LPE-grown Ga1 – xInxAsySb1 – y working wavelength of devices. The problem of solid solutions were obtained using conventional pho- increasing the working wavelength of devices based on tolithographic technology. The mesa (300-µm-diam) and point (100-µm-diam) contacts were formed on the Ga1 – xInxAsySb1 – y solid solutions is still among the most important tasks in optoelectronic technology. wide-bandgap GaSb layer, and a continuous contact was formed on the GaSb substrate (Fig. 1a). The con- It was established [1, 2] that the density of natural tacts on n- and p-type GaSb were made of Cr/Au + defect complexes VGaGaSb in GaSb- and InAS-based Te/Au and Cr/Au + Ge/Au layers, respectively. Finally, solid solutions can be significantly reduced by growing 500 × 500-µm chips were mounted in standard TO-18 epitaxial layers of these solutions from lead-containing cases. melts. Lead does not form compounds with other com- The electroluminescence (EL) characteristics of ponents of the melt and is not included into the solid LEDs were studied using an automated setup based on phase. Previously [3, 4], we have studied the role of lead a DK-480 monochromator (CVI Laser Corp., USA) in the growth of Ga1 – xInxAsySb1 – y solid solutions. Inves- and a liquid-nitrogen-cooled InSb photodiode (Judson tigation of the galvanomagnetic properties of undoped, as Technologies, USA). Signals from the photodetector well as Ge- and Te-doped, Ga1 – xInxAsySb1 – y solid solu- were processed using a synchronous detection scheme tions grown from lead-containing melts confirmed based on an SR 810 lock-in amplifier (SRS Inc., USA). good prospects of using such materials in optoelec- The room-temperature (T = 300 K) EL spectra were tronic devices operating in the 1.8–3 µm range. measured for LEDs powered by a pulsed current with an on-off ratio of Q = 2 at a frequency of 512 Hz. This Letter reports for the first time on light-emit- ting diodes (LEDs) with the maximum emission at LEDs with lmax = 2.3 mm. The active region in λ µ µ max = 2.3 and 2.44 m, based on Ga1 – xInxAsySb1 – y these LEDs was a 2- m-thick Ga1 – xInxAsySb1 – y solid solid solutions grown from lead-containing melts, and solution layer with the indium content x = 0.21 (Eg = presents the results of investigation of the electrolumi- 0.53 eV, T = 300 K) grown on a p-GaSb(100) substrate. nescence spectra of these LEDs. The energy band diagram of the device heterostructure 1063-7850/04/3007-0529 $26.00 © 2004 MAIK “Nauka/Interperiodica” 530 PARKHOMENKO et al. 1 (a) J, a.u. ∅ 100 µm 350 P, mW 2 1.0 (a) 300 0.8 3 0.6 220 mA 0.4 150 mA 250 0.2 η = 1.6% 100 mA 0 100 200 200 I, mA 50 mA 150 Eg, eV (b) 100 0.72 0.53 50 0 1900 2000 2100 2200 2300 2400 2500 2600 -GaSb λ, nm n , a.u. -GaSb(100) J p , µW -GaInAsSb 25 P p 70 60 (b) 2.0 2.5 d, µm 50 20 40 218 mA E , eV g (c) 30 200 mA 20 150 mA 0.72 10 η = 0.11% 15 100 mA 0.51 0 100 200 I, mA 50 mA 10 -GaSb p 5 -GaSb:Te(100) -GaInAsSb n n 1.2 2.5 d, µm 0 2000 2100 2200 2300 2400 2500 26002700 2800 λ, nm Fig. 1. LEDs based on GaSb/Ga1 – xInxAsySb1 – y/GaSb heterostructures: (a) schematic diagram of a mesa structure Fig. 2. Room-temperature EL spectra of LEDs with the indium showing (1) upper contact, (2) emitter, and (3) active region; content in the active region x = 0.21 (a) and 0.25 (b) measured (b, c) energy band diagrams of LEDs with the indium con- for various diode currents I. The insets show plots of the output tent in the active region x = 0.21 and 0.25, respectively. emission power P versus current I for T = 300 K. is depicted in Fig. 1b. The EL spectra with the most emission maximum slightly shifts toward longer wave- intense signals of radiative recombination were lengths with increasing diode current. At a current of obtained for LEDs with undoped active regions. The 220 mA, the shift amounts to 0.02 µm, which is evi- charge carrier density determined from the Hall effect dence of an insignificant effect of the current-induced measurements was p = 3 × 1018 cm–3 at T = 300 K (p = structure heating on the EL characteristics. This con- 4.6 × 1016 cm–3 at T = 77 K). The upper GaSb layer in clusion was confirmed by the absence of pronounced these LEDs was doped with tellurium to n ~ (1–4) × saturation in the plot of the integral optical output 1018 cm–3 (T = 300 K). power versus current (see inset in Fig. 2a) for I up to 220 mA, at which the output power reaches 0.937 mW The current–voltage characteristics of these LEDs and the external quantum yield is η = 1.6%. exhibited a diode character with a room-temperature cutoff voltage of 0.35 V. The serial resistance of direct- LEDs with lmax = 2.44 mm. The active region in Ω µ biased diodes was ~3.1 . these LEDs was a 1.2- m-thick Ga1 – xInxAsySb1 – y Figure 2a shows the spectral characteristics of such solid solution layer with the indium content x = 0.247 LEDs measured at T = 300 K. As can be seen, the EL (Eg = 0.51 eV, T = 300 K) grown on an n-GaSb(100) spectrum exhibits a single band with the maximum at substrate. The energy band diagram of the device het- µ 2.29 m (Eg = 0.54 eV) at a diode current of I = erostructure is depicted in Fig. 1c. The EL spectra with 100 mA. The full width at half maximum (FWHM) of the most intense signals of radiative recombination this EL spectrum is 0.20 µm and exhibits growth with were observed for LEDs in which the active region was the current and reaches 0.23 µm at I = 220 mA. The doped with Te to n = 3 × 1018 cm–3 (T = 300 K). The TECHNICAL PHYSICS LETTERS Vol. 30 No. 7 2004 LIGHT-EMITTING DIODES 531 wide-bandgap emitter was an epitaxial GaSb layer Conclusions. We have succeeded for the first time doped with Ge to p ~ 5 × 1018 cm–3 (T = 300 K). in obtaining LEDs with the maximum emission at λ µ max = 2.3 and 2.44 m based on Ga1 – xInxAsySb1 – y The current–voltage characteristics of these LEDs solid solution layers grown by LPE from lead-contain- exhibited a diode character with a cutoff voltage of ing melts. The room-temperature external quantum 0.4 V at T = 300 K. The serial resistance of direct- µ Ω yield of the 2.3 and 2.44 m LEDs is 1.6 and 0.11%, biased diodes was ~1.7 . respectively. These LEDs can find wide use in systems Figure 2b shows the spectral characteristics of such of ecological monitoring and medical diagnostics. LEDs measured at T = 300 K. As can be seen, the EL µ spectrum exhibit a maximum at 2.44 m corresponding REFERENCES to the bandgap width in the active region (Eg = 0.51 eV).