Increasing Optical Efficiency in the Telecommunication Bands of Strain-Engineered Ga(As,Bi) Alloys

Abstract

The search for semiconducting materials with improved optical properties relies on the possibility to manipulate the semiconductors band structure by using quantum confinement, strain effects, and by the addition of diluted amounts of impurity elements such as Bi. In this study, we explore the possibility to engineer the structural and physical properties of the Ga(As, Bi) alloy by employing different stress conditions in its epitaxial growth. Films with variable concentration of Bi are grown by molecular beam epitaxy on bare GaAs(001) crystals and on partially relaxed (In, Ga)As double buffer layers acting as stressors aiming to control the Bi incorporation into the alloy and improving the optical properties in terms of efficiency. A combination of several structural and electronic characterization techniques and dedicated density-functional-theory calculations allows us a systematic comparison between the samples grown under compressive and tensile strain. We demonstrate the possibility to grow Ga(As, Bi) under different strain conditions without affecting its crystal quality. The different strain conditions strongly impact the Bi incorporation in the GaAs matrix and the luminescence properties of the sample. We find (i) a striking improvement of the photoluminescence with a strongly increased radiative efficiency when Ga(As, Bi) is grown under tensile strain and (ii) an interesting higher redshift with respect to Ga(As, Bi) grown compressively on GaAs. These two effects allow us to reach the important photoluminescence emission at 1.3 µm with a Bi concentration as low as 4.9% compared to 7.5% needed for samples grown directly on GaAs. This is a significant achievement for the application of the Ga(As, Bi) material in optoelectronic devices.

Reflectance anisotropy spectroscopy of strain-engineered GaAsBi alloys

“…From this behavior of RAS sign, we propose that the final (and till now not yet determined) configuration of Bi atoms in high density samples (under tensile growth) is the same as in low density samples (in this case without distinguishing between tensile and compressive growth). We conclude that growth performed under tensile strain manages more efficiently a higher concentration of Bi atoms [11].…”

“…The same does not happen for compressive samples, where at high Bi concentration (at least equal to 7 %) the resulting strain produces a modification of the local structure necessary to relax the energy surplus coming from local deformation of the crystal. Information coming from other techniques (XRD, PL) confirm that sample 1c has a lower crystal quality (as labeled in terms of the optical behavior detected by PL), while at low Bi values compressive samples are of good quality [11]. The general trend suggests that -This is the author's peer reviewed, accepted manuscript.…”

“…A different strategy is based on a choice of the substrate such that the growing GaAsBi layer experiences a tensile strain (for a substrate unit cell larger than the GaAsBi one) instead of the more commonly used compressive strain (for a substrate unit cell smaller than the GaAsBi one, as for GaAsBi grown onto GaAs). It has been demonstrated that in this way a higher quality of the structural and optical properties at the same Bi incorporation is reached [11].…”

Structural and optical properties of n-type and p-type GaAs(1−x)Bi x thin films grown by molecular beam epitaxy on (311)B GaAs substrates

“…Using the above equations, εzz and εxx of both samples are found to be the same and have values of 0.00035 and -0.018, respectively. One can therefore conclude that there is some residual strain in GaAs(1−x)Bix layers [29]. It is important to point out that due to the large size of the spot of X-rays impinging on the samples, the data presented here represent only averaged values of strain.…”

Выращивание слоев GaAs-=SUB=-1-x-=/SUB=-Bi-=SUB=-x-=/SUB=- методом молекулярно-лучевой эпитаксии

“…Наиболее важными из таких приборов являются сверхбыстродействующие фотоприемники, а также генераторы и приемники терагерцового излучения. Оказалось, что уменьшение ширины запрещенной зоны при легировании GaAs висмутом позволяет расширить область спектральной чувствительности оптоэлектронных приборов до длин волн 1.3 мкм и более, соответствующих O-полосе оптоволоконной связи [10]. При этом за счет изменения структуры зон можно существенно понизить избыточный шум лавинных диодов [11] и существенно улучшить характеристики приборов терагерцового диапазона частот [12].…”