JPH02297979A - Light-emitting diode array - Google Patents

Abstract

PURPOSE:To achieve an improved ohmic contact without reducing light-emitting efficiency by using a different material at the time of providing a common electrode as an individual electrode on one and the same surface of a LED array. CONSTITUTION:A light-emitting region 2 is provided in alignment on the surface of a chemical compound semiconductor 1 in an optical printer head using a LED array. An individual electrode 3 which is in ohmic contact with the region 2 is provided on the surface of the substrate 1 through an insulating film. A common electrode 4 in element units which is in ohmic contact with a region other than the region 2 is provided on the surface of this substrate 1. The electrodes 3 and 4 consists of different materials in terms of work function and electron affinity, thus enabling wiring for dynamic drive and power supply to be performed with improved operation without having an undesired contact conduction of neighboring LED arrays and without being restricted by wiring.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a light emitting diode array suitable for optical print heads and the like.

(Example) Conventional technology Conventionally, a light emitting diode array used in an optical printer has a plurality of light emitting regions on the surface of a compound semiconductor substrate, individual electrodes on the front surface, and common electrodes on the back surface, as disclosed in Japanese Patent Application Laid-Open No. 198873/1983. Electrodes were installed. However, wiring the common pole on the back surface is difficult when connecting each light emitting diode array to a scanning drive means, or when providing a power supply section in the center of a long row of light emitting diode arrays.

(c) Problems to be Solved by the Invention Therefore, we considered providing individual electrodes and surface electrodes on the surface of the light emitting diode array. However, even if p and n conductivity type determining metals are mixed into the electrode material, if the main material of each of the individual electrodes and the surface electrode is the same, ohmic contact cannot be obtained and it is generally a Schottky contact. became. For example, Ga
When an electric scratch made mainly of aluminum is provided on the surface of AsP, good ohmic contact is obtained for p-type GaAsP as shown by the solid line (a) in Figure 2, but for n-type it is obtained as shown by the broken line ( As shown in b), a region between <+0.7V and -13V occurs where it is extremely difficult for current to flow, which is not preferable.

(d) Means for Solving the Problems The present invention has been made to correct the above points, and focuses on work function and electron affinity, and when providing individual electrodes and common electrodes on the same surface, the main material is For example, in contrast to GaAsP, the main material of the individual electrodes is aluminum, and the main material of the common electrode is gold or silver.

(e) Effect This allows the individual i-poles and the common electrode to be provided on the same surface with good ohmic properties.

Embodiment Figure 1 is a perspective view of the main parts of an optical print head using a light emitting diode array according to an embodiment of the present invention. (1) is a compound semiconductor substrate, for example, GaAs! : Made of epitaxially grown GaAsP. On the GaAsP surface of the substrate (1), light emitting regions (2) are arranged in a line by selective diffusion or the like. (3) is an electrode (individual electrode) provided on the surface of the substrate (1) via an insulating film and in ohmic contact with the light emitting region (2).
It is.

(1) is provided on the surface of the substrate (1), and is a common pole of the element unit that is in ohmic contact with a region other than the light emitting region on the surface of the substrate. The electrode (3) and the common electrode (41) are made of different materials as will be described later. This type of light emitting diode array is mounted on an insulated base (5) with good heat dissipation.
etc., with a silicon heat conductive rubber (6), etc., and wiring is provided to the drive circuit element (7) directly or via a conductive pattern, etc. by a wire bonding method, a tape carrier method, etc.

Electrodes of such a light emitting diode array (3) Common electrode (
4), for example, aluminum (A2) and gold (A u
), its work function is A11.20 (eV)
, A u : 4.58 (e V ). Therefore, if only the work function is considered, Au or a material mainly composed of Au has a higher Schottky barrier than A2 or an alloy mainly composed of A2. However, since the rate of alloying of Au with GaAsP is fast, good ohmic contact can be obtained if the energy band is caused to degenerate in consideration of electron affinity. On the other hand, it is possible to increase the impurity concentration of an ohmic semiconductor to facilitate ohmic contact, but this method cannot be used for compound semiconductor light-emitting diodes because increasing the impurity concentration lowers the luminous efficiency. In the case of n-type GaAsP, the Te concentration is 2.0.
~20. OX IQ' is "cm-'.

As a result of these studies, it was found that a p-type Zn diffusion layer (with an impurity concentration of 1 to IOX
AN or 5iSCu with At of 95% or more for
, Cu-5i, etc. are used to form (individual) electrodes, and Au-5n-Te is formed on the surface of the n-type epitaxial layer.
(98:1:1) is used to form the common electrode.

In addition, as a common electrode provided on the same surface as the AX-based individual electrodes, Au-Ge-N (88; 12: 5), Ag
Even when an alloy of -In-Ge (8:1:1) or a combination thereof, or an alloy in which a small amount of conductivity type impurity was added to these, almost no Schottky barrier was generated.

(g) Effects of the invention As described above, when providing the individual electrodes and the common electrode on the same surface of the light emitting diode array, different materials are used with a focus on work function and electron affinity, so that the light emitting efficiency is not reduced. A good ohmic contact can be obtained, which eliminates undesirable contact conduction of adjacent light emitting diode arrays and restrictions on wiring, allowing dynamic drive wiring and power supply to be performed with ease.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the main parts of an optical print head using a light emitting diode array according to an embodiment of the present invention, and FIG.
FIG. 3 is a current-voltage characteristic diagram between the electrode and the electrode.

Claims (1)

[Claims] 1) A compound semiconductor substrate having a plurality of light emitting regions aligned on its surface, and an individual electrode made of a first material provided on the surface of the substrate and in ohmic contact with the light emitting regions. and a common electrode made of a second material different from the first material provided on the surface of the substrate and in ohmic contact with a region other than the light emitting region of the substrate. 2) The substrate is GaAsP/GaAs, and the first
2. The light emitting diode array according to claim 1, wherein the material is mainly aluminum, and the second material is mainly gold or silver.