InAs flip-chip LEDs with InGaAsSb buffer layers
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F SEMICONDUCTOR DEVICES
InAs Flip-Chip LEDs with InGaAsSb Buffer Layers N. V. Zotovaa, N. D. Il’inskayaa, S. A. Karandasheva, B. A. Matveeva^, M. A. Remennyœa, N. M. Stus’a, V. V. Shustova, and N. G. Tarakanovab aIoffe
Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected] bIoffe LED, Ltd., St. Petersburg, 194021 Russia Received December 19, 2005; accepted for publication December 30, 2005
Abstract—Under study are the electrical and optical properties of n-InGaAsSb epitaxial layers with composition close to InAs and lattice-matched with it, fabricated on InAs substrates by LPE from Te-containing melts. The layers are transparent in the 3-µm range owing to the Moss-Burstein effect. The light–current characteristics and near-field emission pattern of InAs-based flip-chip LEDs with the emission extracted through n+-InGaAsSb layers are presented and discussed. PACS numbers: 85.60.Jb, 78.40.Fy DOI: 10.1134/S1063782606080173
1. INTRODUCTION In the last decade, considerable progress has been achieved in the development of uncooled LEDs and lasers emitting in the mid-IR (3–6 µm) spectral range, intended for testing of photodetector systems and for measurements of the transmission of the atmosphere to control the content of noxious components, e.g., nitrogen oxide [1]. The most successful device implementations of LEDs use transparent substrates, which simplifies the design of optically excited sources in the case of photoluminescence in a “transmission configuration” and makes possible the flip-chip configuration with electric injection of carriers, e.g., with the use of heavily doped n+-InSb substrates [2]. Heavily doped InAs with the electron density n > 1018 cm–3 has been shown to be applicable as a substrate material for photodetectors [3, 4] and optically [5] and electrically [4] excited IR light sources with a working wavelength of ~3 µm. At this carrier density, electrons in the conduction band are degenerate and the absorption edge is blue-shifted due to the Moss–Burstein effect. At the same time, the overwhelming majority of manufacturers do not include data on the transparency spectra into the specification sheets for InAs substrates, which gives no way of making a correct choice of a material for fabrication and study of diodes with the emission extracted through the substrate in the wavelength range 2.9–3.4 µm. In this situation, a topical task is to study the transparency of solid solutions approximately lattice-matched with InAs, which might be used to form a buffer layer between the light-emitting surface and active layer with the working wavelength λ = 2.9–3.4 µm. If this layer is thick enough to provide the mechanical strength of a heterostructure, the nontransparent n-InAs substrate can be eventually removed by chemical etching. In its
optical properties, this heterostructure with the n-InAs part removed is similar to the n+-InAs/n-InAsSbP/nInAs/p-InAsSbP structure described in our earlier papers [3, 4], and can be regarded as its alter
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