Electroabsorption inIn0.53Ga0.47As/

Richard P. Leavitt

¹

,

J. W. Little

²

,

S. C. Horst

³

Abstract

We report the results of photocurrent measurements on Ino 53Gao 47As/Ino»Alo 4, As asymmetric coupled quantum wells lattice matched to InP substrates. We show that large shifts in excitonic absorptions with applied bias result from the resonant coupling of electron subbands. Results of our measurements agree well with calculations performed with use of a single-band envelope-function approximation that incorporates a scatteringphase-shift method for determining the quasibound electronand hole-subband states of the coupled-well system in an electric field. The rapid development of fiber-optic communications systems has stimulated a search for semiconductor electro-optic devices that operate in the 1.3and 1.55-pm wavelength bands. Effects that have been thoroughly characterized' in GaAs/Al Ga, "As multiple quantum wells (MQW's) are now being investigated in the Inp 53Gap 47As/Inp 5@Alp 4sAs (Refs. 5 -7) and Inp 53Gap 47As/InP (Refs. 8 and 9) quantum-well systems lattice matched to InP substrates. Many of the electrooptic devices being studied are based on an electric-fieldinduced shift in excitonic absorption peaks known as the quantum-confined Stark effect (QCSE). ' However, the magnitude of the QCSE depends strongly on the well thicknesses (for isolated, rectangular wells) and can be very small for the relatively thin wells (3 -8 nm) requiredfor implementation in devices that operate at 1.3 and 1.55 pm. The development of effective quantum-well modulators for these wavelengths will depend on identifying new electroabsorption mechanisms that are not subject to this limitation.In this Brief Report we show that asymmetric coupled quantum wells (ACQW's), in which two Inp 53Gap47As quantum wells of different thicknesses are coupled by a thin Inp5zAlp4sAs tunnel barrier (see Fig. 1), exhibit significant electroabsorption effects even when the wells are relatively thin. Previously, we demonstrated that the coupling of the lowest-energy electron subbands in a GaAs/Al Ga, As ACQW structure could be clearly observed in low-temperature photocurrent (PC) spectroscopy and resulted in enhanced intensity and phase modulation in waveguides. ' Here we report the results of roomand low-temperature PC measurements on two Inp 53Gap 47As/Inp 5pAlp 4sAs MQW samples: one containing uncoupled quantum wells and one containing the ACQW structure. We show that the shifts in the excitonic absorption peaks in the ACQW structure are large even for low biases, whereas the Stark shifts observed in the uncoupled-well sample are relatively small. The InQ 53GaQ 47As/Inp g2Alp 48As samples studied in this work were grown by molecular-beam epitaxy on n+-type InP substrates at a growth temperature of 520 C at a rate of 1 2 pm/h, with the group V (As4)togroup-III beam-flux ratio maintained at about 5:1. The layer sequence for the samples, starting from the substrate, is as follows: 0.35 pm n +-type (-2 X 10' /cm Si) Inp 5&Alp 4sAs; 0.15 pm undoped Inp 52Alp «As; 0.7 pm undoped MQW region; 0.15 pm undoped Inp &&Alp 4sAs; 0.2 pm p+-type ( -2X 10' /cmBe)...

<title>Electroabsorption and carrier dynamics in (Ga,In)As/(Al,In)As asymmetric double quantum wells</title>

“…In undoped (Ga,In)As/(Al,In)As coupled quantum well systems consisting of similar well widths, excitonic absorption features persist to much higher applied fields than those considered in this work. [5] Hence, the observed absorption changes can only arise from the real-space transfer of electrons from the WW to the NW. To further investigate the electron densities in both the WW and NW, we measured the 50 K photolum.inescence (PL) spectra at different applied fields (see Fig.…”

“…The use of electron transfer between a quatemary reservoir and single quantum well and the use of coupled quantum wells have been shown to be attractive alternatives for optical fiber compatible device applications. [3][4][5] Although recent results utilizing the (Ga,Al,In)As/(Al,In)As on InP system have demonstrated improved material quality and device performance at these wavelengths [6-81, improvements in the electro-optic characteristics of these materials is still required. In this paper, we demonstrate a novel electroabsorption mechanism based on selective doping of (Ga,In)As/(Al,In)As Asymmetric Double Quantum Wells (ADQWs).…”

Response to ‘‘Comment on ‘Optical bistability in self-electro-optic effect devices with asymmetric quantum wells’ and on ‘Novel configuration of self-electro-optic effect device based on asymmetric quantum wells’ ’’ [Appl. Phys. Lett. 5 7, 1363 (1990)]

“…A similar "effective" blue shift bistability has also been demonstrated from Wannier-Stark localization in a superlattice. 5 The other method suggested by LL, namely, the use of piezoelectric fields in strained [Ill] quantum wells to asymmetrize the well, was recently demonstrated in InGaAs/GaAs wells on a [111] GaAs substrate,f' with clear bistability observed.…”