JP3969182B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device.
[0002]
[Prior art]
Xerographic printers using LEDs (light emitting diodes) have been put into practical use. In the xerographic method, it is necessary to select an LED having a light emission wavelength and light emission intensity required from the light receiving sensitivity of the photosensitive drum.
[0003]
Practically, those using GaAsP as the main material of the p / n junction and those using AlGaAs as the main material of the p / n junction are employed.
[0004]
In an AlGaAs-based infrared LED, a so-called bulk type active layer made of AlGaAs and having a thickness of about 0.5 μm to 2 μm has been adopted as an active layer where light emission occurs. The emission wavelength can be adjusted to a desired wavelength by the AlAs mixed crystal ratio of the active layer.
[0005]
[Problems to be solved by the invention]
By the way, since the light emission output of the AlGaAs LED array for LED printers directly affects the printing speed, it is desired to have a high output, and a multiple reflection film or the like is used to increase the light extraction efficiency. Although it has been devised, there has been a problem that the luminous efficiency of the active layer for converting current into light is low.
[0006]
Accordingly, an object of the present invention is to solve the above-described problems and provide a semiconductor light emitting device having high light emission efficiency.
[0007]
[Means for Solving the Problems]
To achieve the above object, the invention of claim 1 is directed to an n-type GaAs buffer layer on an n-type GaAs substrate, a multi-reflection film comprising an n-type AlGaAs pair having different Al composition ratios, and an n-type AlGaAs lower portion. cladding layer, p-type or multi-quantum well active layer made of undoped AlGaAs, in the semiconductor light emitting device having a p-type AlGaAs upper cladding layer and the p-type stacked structure in which a GaAs contact layer are successively epitaxially grown in, the multiple quantum well active The thickness of the well layer and the barrier layer is 4 nm to 15 nm, the AlAs mixed crystal ratio of the well layer is X1, the AlAs mixed crystal ratio of the barrier layer is X2, and X2−X1 ≧ 0. when two light emission output the well layer of the multiple quantum well active layer and the number of pairs of the barrier layer as 50 to 150 pairs it with maximum One in which was adjusted to.
[0014]
The present inventors have found that the light emission output is changed by changing the number of pairs of the well layer and the barrier layer of the AlGaAs multiple quantum well active layer. In particular, it has been found that the maximum value of the light emission output exists within the range of 10 to 150 pairs of well layers and barrier layers. As a result, by adjusting the number of pairs, it is possible to provide a semiconductor light emitting element with high light emission efficiency.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0016]
FIG. 1 is a cross-sectional view showing an embodiment of a semiconductor light emitting device of the present invention.
[0017]
This semiconductor light emitting device comprises an n-type GaAs buffer layer 2 and an n-type Al _0.25 Ga _0.75 As / Al _0.85 Ga _0.15 As layer 12 pair on an n-type GaAs substrate 1. Multiple reflection film 3, n-type AlGaAs lower cladding layer 4, multiple quantum well active layer 5 having 75 pairs of AlGaAs well (well) / barrier layers, p-type AlGaAs upper cladding layer 6 and p-type GaAs The contact layer 7 is epitaxially grown and laminated, the n-side common electrode (cathode) 8 is formed on the GaAs substrate 1 of the obtained laminate, and the p-side ohmic contact electrode (anode) 9 is formed on the GaAs contact layer 7 It is. This figure shows one LED portion of the LED array, and 10 indicates a light emitting portion.
[0018]
These epitaxial layers are grown by the MOVPE method. The growth temperature at that time was about 700 ° C. (substrate temperature), the growth pressure was 70 Torr, and trimethylgallium and trimethylaluminum were used as Group III raw materials. Arsine was used as the Group V raw material. Hydrogen selenide was used as the n-type dopant, and diethylzinc (dimethylzinc may be used) as the p-type dopant.
[0019]
The number of pairs of well layers and barrier layers of the multi-quantum well active layer 5 is preferably 50 to 150 pairs , and the thickness thereof is preferably in the range of 4 nm to 15 nm.
[0020]
Further, it is preferable that the AlAs mixed crystal ratio of the well layer is X1, the AlAs mixed crystal ratio of the barrier layer is X2, and X2−X1 ≧ 0.2.
[0021]
When a plurality of light emitting units 10 are formed, it is preferable that the density of each light emitting unit 10 is 240 dpi or more and the size is 50 μm × 50 μm or less. Alternatively, the contact layer 7 on each light emitting unit 10 may have a size of 20 μm × 20 μm or less, and the anode may be individually connected so as to have an ohmic contact with a part of the contact layer 7. Further, the light emitting units 10 may be arranged in at least one row.
[0022]
The anodes may be arranged from one side of the arrangement so as to be orthogonal to the arrangement direction of the light emitting units 10 or may be arranged alternately from both sides of the arrangement.
[0023]
Next, a prototype LED array with 600 dpi and a light emission wavelength of 740 nm was produced. As shown in FIG. 2, when the number of well / barrier layer pairs of the AlGaAs multiple quantum well active layer 5 is a variable, the maximum light emission is about 75 pairs. Output was obtained.
[0024]
FIG. 2 is a diagram showing the relationship between the number of pairs in the multi-quantum well active layer and the normalized light output. The horizontal axis indicates the number of pairs in the multi-quantum well active layer, and the vertical axis indicates the normalized light output.
[0025]
As described above, the LED array type light emitting device of the present invention employs a multiple quantum well active layer comprising a pair of an AlGaAs well and a barrier layer, and the number of pairs is 50 to 150 pairs to maximize luminous efficiency. The multi-quantum well active layer thus optimized can provide high luminous efficiency.
[0026]
Here, in the above-described embodiment, the p-side-up LED array has been described as an example. However, the present invention can also be applied to an n-side-up LED array formed on a p-type GaAs substrate.
[0027]
In addition, the p-type dopant of the epitaxial layer may be Zn, Mg, C, or a combination thereof, and the n-type dopant may be Se, Si, Te, or a combination thereof.
[0028]
【The invention's effect】
In short, according to the present invention, it is possible to realize a semiconductor light emitting device with high luminous efficiency.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a semiconductor light emitting device of the present invention.
FIG. 2 is a diagram showing the relationship between the number of pairs of multiple quantum well active layers and the normalized light emission output.
[Explanation of symbols]
1 n-type GaAs substrate 2 n-type buffer layer 3 n-type AlGaAs / AlGaAs multiple reflection film 4 n-type lower cladding layer 5 multiple quantum well active layer 6 p-type AlGaAs upper cladding layer 7 p-type GaAs contact layer 8 n-side common electrode (cathode)
9 p-side ohmic contact electrode (anode)
10 Light emitting part

Claims (1)

An n-type GaAs buffer layer on an n-type GaAs substrate, a multiple reflection film made of an n-type AlGaAs pair having a different Al composition ratio, an n-type AlGaAs lower cladding layer, and a multiple quantum well made of p-type or undoped AlGaAs In a semiconductor light emitting device having a stacked structure in which an active layer, a p-type AlGaAs upper cladding layer, and a p-type GaAs contact layer are sequentially epitaxially grown , the thickness of the well layer and the barrier layer of the multiple quantum well active layer is 4 nm to 15 nm. When the AlAs mixed crystal ratio of the well layer is X1, the AlAs mixed crystal ratio of the barrier layer is X2, and X2−X1 ≧ 0.2, the well of the multiple quantum well active layer semiconductor light-emitting output the number of pairs layer and the barrier layer as 50 to 150 pairs, characterized in that adjusted to maximize Child.

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