Gallium Nitride Multioperate Optoelectronic Devices
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ABSTRACT Opportunity of creation of several optoelectronic devices such as optron, photoreceiver, switch device, IR-to-visible signal transformer and others based on i-n-GaN light emitting diodes (LED) is shown. Technology and properties of GaN LED in relation to the desired device properties are discussed. A discussion of issues relating to electrical and optical positive feed back between the device elements is also included. INTRODUCTION Optoelectronic devices discussed in this paper are known as optrons. Optron constructions and principles of work are well known and widely described in scientific literature. For example [1]. The functional problems that occurred in the most number of optron types are caused by hybrid technology - the way those types are manufactured. We offer to discuss the optrons created in monolith crystal on a single substrate. They are smaller, more reliable, and usually multifunctional. Electrical and optical positive feed back between the optopaire elements allows to create the devices with S-shape voltage-current characteristic (VCC) and therefore enlarge optron functions. These devices appeared to be bi-stable (due to mentioned positive feed back) and may be widely used in automatic communicational systems as switch devices, transformers, amplifiers, and generators of optical and electrical signals. All presented optron are created on i-n-GaN LED base. High resistance i-layer serves as a "substrate" for additional functional layers depositing and allows to construct desired properties. The GaN layer doped with zinc and oxygen simultaneously is used in the active area of LED. It gives sufficient efficiency to LEDs and to the devices created on their base. EXPERIMENT AND RESULTS I-n-GaN Light Emitting Diodes The i-n-GaN LED with an active area made of GaN doped with zinc and oxygen simultaneously is the common and the main part of all optoelectronic devices described in this paper. LED consists of 3-layer GaN structure grown on sapphire (1020) substrate and oriented in (1120) plane (Fig.1.).The epitaxial layers are grown by gas-phase method in chloride-hydride system. The undoped n-GaN layer is grown at 1050'C substrate temperature with 20 jim/hr rate which gives fairly good structural quality to it and to the layers that are grown on its base. The 1137
Mat. Res. Soc. Symp. Proc. Vol. 482 © 1998 Materials Research Society
n-GaN layer thickness is 10-20 jim and its resistance is about 10-3 D.cm. Then two layers: GaN doped with zinc and oxygen simultaneously (thickness 0.3-3 gim; resistance 103-105 Q.cm) and GaN doped only with zinc (thickness - 0.05-0.5 gm; resistance 105-107 n.sm) are grown at temperature 950'C. Layers' parameters are chosen in terms of having i-GaN(Zn) layer full resistance 10 times as much or more as i÷-GaN(Zn,O) layer one.At these layers resistance values almost all voltage applied to the structure drops on i-GaN(Zn) layer. If full applied voltage is 440 V the electric field in i-GaN(Zn) layer is 105 V/cm and bigger, and electrons gain enough energy in it to excite
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