JPH0645645A - Light-emitting element - Google Patents

Abstract

PURPOSE:To provide a light-emitting element wherein the increase rate of the amount of light with reference to an increase in an electric current can be made definite and the amount of light is easy to control when the element is used in various kinds of apparatuses in the light-emitting element wherein the element is provided with the junction part of a P-type semiconductor to an N-type semiconductor and a junction face emits light by applying a voltage in the forward direction to the junction face. CONSTITUTION:An inner-layer part and a surface-layer part, in which the mixed crystal ratio of phosphorus is different from each other, are formed in an N-type semiconductor 1, zinc is diffused to a prescribed region by using a selective diffused film 5, a P-type semiconductor 2 is formed, an N-type semiconductor 1a and a P-type semiconductor 1b, whose forbidden band width is larger than that of an N-type semiconductor 2a and a P-type semiconductor 2b at the inner- layer part, are formed, a positive electrode 3 is formed on the surface of the P-type semiconductor 2 and a negative electrode 4 is formed on the rear of the N-type electrode 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and more particularly to a surface emitting type light emitting device.

[0002]

2. Description of the Related Art Light emitting devices that are small and lightweight are widely used in various fields. In recent years, light emitting elements have been used in optical printers that record information by light irradiation, image readers that read images and bar code data using the reflection intensity of light, or optical communication devices that use optical signals. There is.

FIG. 6 is a schematic sectional view showing the structure of a conventional light emitting element, and FIG. 7 is a schematic plan view of a conventional light emitting element.

In the light emitting device shown in FIGS. 6 and 7, the gallium arsenide phosphide semiconductor containing tellurium forms the first conductivity type substrate, that is, the N type semiconductor 1. Zinc is diffused in the N-type semiconductor 1 to form a second conductivity type diffusion layer, that is, a P-type gallium arsenide phosphide semiconductor 2 (hereinafter referred to as P-type semiconductor 2). When zinc is diffused into the N-type semiconductor 1, the upper surface of the N-type semiconductor 1 is masked by a selective diffusion film 5 having a diffusion window, and diffusion is performed from the diffusion window. 2 can be formed.

A positive electrode 3 is formed on the upper surface of the P-type semiconductor 2.
Is provided, the negative electrode 4 is formed on the back surface of the N-type semiconductor 1, a forward voltage is applied to the junction surface of the P-type semiconductor 2 and the N-type semiconductor 1, and the diffused majority carriers are diffused. Electric energy is converted into light energy and light is emitted.

[0006]

However, the above-mentioned P
When a forward voltage is applied to the PN junction surface of the light emitting element having an N junction surface, the current flowing through the light emitting element flows in the entire PN junction surface as shown in FIG. The relationship between the current flowing through the light emitting element and the light output at this time is as shown by the solid line in FIG.
In a region where the current is small, the rate of increase in light output with increase in current is not constant, and the rate of increase in light output with increase in current strongly depends on the current. (Here, in order to clarify the difference from the solid line in which the increase rate is not constant, a broken line shows a case where the relationship between the current and the light amount is linear.)
That is, when the voltage applied to the PN junction surface is V, the current flowing is a component proportional to exp (eV / kT) (hereinafter referred to as component A) and a component proportional to exp (eV / 2kT) (hereinafter referred to as component B). Called). Here, the amount of light emitted from the light emitting element is proportional to the current component A.

In the region where the current is large, the component A occupies most of the total current, and the amount of light emitted from the light emitting element is proportional to the component A. Therefore, the rate of increase of the amount of light with respect to the increase of the current becomes constant. .

That is, in the region where the current is large, the ratio of the current to the light output does not depend on the current value and becomes stable, but in the region where the current is small, the ratio of the component B is relatively large, and the component A and the component Since the ratio of B depends on the voltage, the rate of increase in the amount of light with respect to the increase in current is not constant. here,
The main component of the current component B is the recombination current of electrons and holes that occurs in the depletion layer near the PN junction surface exposed on the semiconductor surface.

In the light emitting element, if the rate of increase of the light quantity with respect to the increase of the current is not constant, there is a problem in the controllability of the light quantity due to the current, and it is difficult to control when used as a light source of an optical printer, an image reader or an optical communication device. There was a problem.

Therefore, an object of the present invention is to provide a light emitting element in which the rate of increase of the light quantity with respect to the increase of the current becomes constant and the light quantity can be easily controlled when used in various devices.

[0011]

In order to solve the above problems, the present invention provides a first conductivity type substrate and a second conductivity type diffusion layer formed on a part of the substrate by impurity diffusion.
In the light-emitting element that includes a forward voltage applied between the electrodes formed on the surface of the base and the diffusion layer to emit light at the bonding surface between the base and the diffusion layer, the base and the diffusion layer include It is composed of a mixed crystal of ternary or more elements, and the base and the diffusion layer have at least one surface layer portion having a mixed crystal ratio different from that of each main body on the surface portion, and at least the surface layer portion The forbidden band width value is set to be larger than the forbidden band width value of each main body, and the light emitting junction surface is deeper than the surface layer portion.

[0012]

In the present invention, the inner layer portion and the surface layer portion having different mixed crystal ratios are formed on the first conductive type substrate and the second conductive type diffusion layer of the light emitting device, and the forbidden band width value is the inner layer. Set so that the surface layer portion is larger than the portion, the current flowing into the depletion layer in the vicinity of the junction between the exposed substrate and the diffusion layer, which is the surface layer portion, is reduced, and the electrons in the depletion layer are By suppressing the recombination of holes, it is possible to suppress the generation of a current component that is not involved in light emission, so that the rate of increase in the amount of light with respect to the increase in the current flowing through the light emitting element becomes constant.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to the drawings.

As a first embodiment, in a light emitting device according to the present invention, a gallium arsenide phosphide semiconductor containing tellurium forms an N-type semiconductor 1 as shown in the schematic sectional view of FIG. Zinc is diffused into a desired region by the diffusion selection film 5 provided on the upper surface of the P-type semiconductor to form a P-type gallium arsenide phosphide semiconductor (hereinafter referred to as P-type semiconductor 2).
In addition, a positive electrode 3 is formed on the upper surface of the P-type semiconductor 2,
A negative electrode 4 is formed on the back surface of the N-type semiconductor 1.

A feature of the present invention is that, as shown in FIG. 1, the light emitting device has a surface layer portion in which the mixed crystal ratio of phosphorus in the crystal is larger than that of the N type semiconductor 1b and the P type semiconductor 2b which are the inner layer portions. A certain N-type semiconductor 1a and a P-type semiconductor 2a, and the forbidden band width of the surface layer portion is formed larger than the forbidden band width of the inner layer portion.

FIG. 2 shows the N-type semiconductor 1 before zinc diffusion.
The N-type semiconductor 1 is formed of two layers having different mixed crystal ratios of phosphorus in the crystal, and forms an N-type semiconductor 1a which is a surface layer portion having a larger mixed crystal ratio of phosphorus than the N-type semiconductor 1b which is an inner layer portion. . Next, zinc is diffused into a desired region by the diffusion selection film 5 having a diffusion port provided on the upper surface of the N-type semiconductor 1a.

Therefore, in the surface layer portion of the light emitting device, the N-type semiconductor 1b and the P-type semiconductor 2b in which the mixed crystal ratio of phosphorus is the inner layer portion.
Larger N-type semiconductor 1a and P-type semiconductor 2a are formed.

The operation state of the light emitting device having the two-layer structure formed as described above will be described.

The current flowing through the light emitting element is a component proportional to exp (eV / kT) (hereinafter component A), where V is the voltage applied to the PN junction surface where the P-type semiconductor 2 and the N-type semiconductor 1 are joined.
, And a component proportional to exp (eV / 2kT) (hereinafter component B
Called). The amount of light emitted from the light emitting element is proportional to the current component A.

When the current is large, that is, in the region where the voltage V is large, the component A occupies the majority of the total current.

Therefore, since the amount of light emitted from the light emitting element is proportional to the component A, the rate of increase in the amount of light with respect to the increase in current becomes constant. That is, in the region where the voltage V is large, the ratio of the current to the light output does not depend on the current value and becomes stable.

Next, when the current value is small, that is, in the region where the voltage V is small, the ratio of the component B is relatively large,
Since the ratio of the component A and the component B depends on the voltage, the rate of increase in the amount of light with respect to the increase in current is not constant. That is, in the region where the voltage V is small, the ratio of the current to the light output depends on the current value. Here, the main component of the current component B is the recombination current of electrons and holes that occurs in the depletion layer near the PN junction surface exposed on the surface of the light emitting element.

Therefore, if the current flowing near the PN junction surface exposed on the surface of the light emitting element, that is, the surface layer portion is suppressed,
The generated current component B can be reduced.

By the way, the current I flowing through the light emitting element can be broadly expressed as the sum of the diffusion current I _d and the recombination current I _r as follows.

I = I _d + I _r ··· Equation 1 Further, it is known that the diffusion current I _d can be expressed by the following equation when the saturation current is I _s with respect to the applied voltage V.

I _d = I _s {exp (qV / kT) −1} ... Equation 2 where q is elementary charge, k is Boltzmann constant, and T is absolute temperature.

Further, it is known that the saturation current I _s can be expressed by the following equation by the minority carrier densities in thermal equilibrium in N, P type semiconductors: N _p , P _n .

I _s = qS (N _p · D _p / L _p + N _n · D _n / L _n ) · Equation 3 Here, S is a PN junction area, L _p and L _n are holes and electrons, respectively. Diffusion lengths, D _p and D _n are diffusion coefficients of holes and electrons, respectively.

Also, according to Boltzmann statistics, the minority carrier densities N _p and P _n are pseudo-Fermi energies: Ef _n and Ef.
It is known that the energies of _p , the conduction band, and the valence band are Ec and Ev, which can be expressed by the following equations.

P _n = Nv · exp {− (Ef _n −Ev) / kT} ··· Equation 4 N _p = Nc · exp {-(Ec-Ef _p ) / kT} ··· Equation 5 Here Where Nv and Nc are the effective densities of valence band and conduction band.

Further, it is known that the following proportional relationship is approximately established when the forbidden band width of a semiconductor is Eg.

(Ef _n −Ev) or (Ec−Ef _p ) ∝Eg Equation 6 Therefore, the following relationships are derived from Equation 4, Equation 5, and Equation 6.

P _n or N _p ∝ exp (−Eg / kT) Equation 7 That is, according to Equations 3 and 7, when the semiconductor band gap Eg increases, the saturation current I _s decreases and the diffusion spreads from Equation 2. The current I _d becomes smaller.

Next, it is known that the recombination current I _r can be expressed by the following equation with respect to the applied voltage V, where the diffusion potential V _d is used.

I _r = (n _i / τ) {kT / (V _d −V)} · W · exp (qV / 2k T) ··· Equation 8 Here, n _i is the carrier density in the intrinsic state, τ is the carrier lifetime, and W is the width of the transition region.

It is known that the diffusion potential V _d can be expressed by the following equation using the pseudo-Fermi energy Ef _n and the valence band energy Ev.

V _d = Ef _n −Ev + kT · ln (P _p / N _v ) · Equation 9 Here, N _v is the effective state density of the valence band, and P _p
Is the density of holes, which are the majority carriers in the P-type semiconductor, and N _v is the effective density of states in the valence band.

Therefore, the following relation can be derived from the equation 9 using the proportional relation of the equation 6.

V _d ∝ Eg (Equation 10) Therefore, from the equations (8), (9) and (10), the forbidden band width Eg of the semiconductor is calculated.
Becomes larger, the recombination current I _r becomes smaller.

That is, the current flowing through the PN junction surface of a semiconductor having a large forbidden band width is smaller than the current flowing through the PN junction surface of a semiconductor having a small forbidden band width for the same applied voltage.

It is generally known that the forbidden band width of a gallium arsenide phosphide semiconductor increases in proportion to the mixed crystal ratio of phosphorus (Begers law).

Therefore, the crystal forming the light emitting device is formed with the surface layer portion having a different phosphorus mixed crystal ratio and the inner layer portion, and the mixed crystal ratio is set so that the surface layer portion is larger than the inner layer portion. By forming the forbidden band width of the surface layer portion higher than the forbidden band width of the inner layer portion, the current flowing into the surface layer portion can be suppressed.

That is, as shown in FIG. 3, the current component I ₁ flowing through the surface layer portion having a large phosphorus mixed crystal ratio, that is, the N-type semiconductor 1a and the P-type semiconductor 2a having a large forbidden band width is
It becomes smaller than the current component I ₂ flowing through the inner layer portion having a small mixed crystal ratio of phosphorus, that is, the N-type semiconductor 1b and the P-type semiconductor 2b having a small forbidden band width.

Therefore, it is possible to suppress the generation of a current component that does not participate in light emission and flows in the vicinity of the PN junction surface exposed on the surface of the light emitting element. Therefore, as shown by the solid line in FIG. The rate of increase of the amount of light with respect to the increase of the flowing current can be made constant.

In the embodiment, the P-type semiconductor 1a having a large phosphorus mixed crystal ratio and the P-type semiconductor 1 having a small phosphorus mixed crystal ratio are used.
Although a hetero barrier exists between b and b due to the difference in mixed crystal ratio, since both P-type semiconductors 1a and 1b are P-type, they hardly act as potential barriers for holes that are majority carriers.

A second embodiment based on the present invention will be described with reference to FIG.

In the first embodiment, the case where the gallium arsenide phosphide semiconductor has a two-layer structure in which the mixed crystal ratio of phosphorus is different has been described, but the present invention is not limited to the two-layer structure, and as shown in FIG. It may be formed from a three-layer structure having different mixed crystal ratios.

As in the first embodiment, the mixed crystal ratio of phosphorus in the surface layer portion is the largest on the surface, and becomes smaller toward the inner layer portion. That is, the N-type semiconductors 1a, 1b, 1c and P
By forming the type semiconductors 2a, 2b, and 2c so that the mixed crystal ratio of phosphorus decreases in order, the same effect as that of the first embodiment can be expected. Furthermore, by reducing the difference in the mixed crystal ratio of phosphorus between the layers, the boundary between the layers of the N-type semiconductor 1a and the N-type semiconductor 1b, and the layer of the N-type semiconductor 1b and the N-type semiconductor 1c. The stress acting on the boundary part of can be reduced. That is, by forming the layers having different mixed crystal ratios, it is possible to reduce the stress between the layers caused by the change in the lattice constant of each layer. In this case, the N-type semiconductor 1b and the P-type semiconductor 2b in the surface layer second layer in FIG. 5 have an effect as a buffer layer for the inner layer section N-type semiconductor 1c and P-type semiconductor 2c, In the structure of the light emitting device, misfit dislocations on the boundary surface can be reduced.

In the above embodiment, the diffusion type light emitting device in which the P-type impurity is diffused into the N-type semiconductor to form the P-type semiconductor has been described. However, the N-type impurity is diffused into the P-type semiconductor to form the N-type semiconductor. You may. The semiconductor material is not limited to gallium arsenide phosphide and may be aluminum gallium arsenide. Furthermore, the present invention is not limited to a ternary mixed crystal such as gallium arsenide and phosphorus, but is also applicable to a quaternary mixed crystal such as indium gallium arsenide and phosphorus. Further, in the above-mentioned embodiment, the method of diffusing the impurities to form the P-type semiconductor has been described, but the method of diffusing the impurities is not limited to the above-mentioned method, and for example, the P-type semiconductor is formed by the ion implantation method. Good.

Further, although the present invention has been described in the above embodiment using the light emitting device having the PN junction, the present invention is not limited to the PN junction and can be used for a PIN junction, for example.

[0051]

According to the light emitting device of the present invention, the rate of increase in the amount of light with respect to the increase in current can be kept constant, so that a light emitting device with good controllability can be manufactured.

Therefore, when the light emitting device of the present invention is used as an exposure light source for an electrophotographic printer, it is possible to realize an exposure device in which the amount of light can be easily controlled by a current. Further, a device that can be easily controlled when used as a light source of an image reader becomes possible. Further, even when the light emitting device according to the present invention is used as a light source of an optical communication device, a device that can be easily controlled can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic sectional view illustrating a first embodiment of a light emitting device according to the present invention.

FIG. 2 is a schematic plan view of an N-type semiconductor substrate before zinc diffusion for explaining a first embodiment of a light emitting device according to the present invention.

FIG. 3 is a schematic diagram showing a current distribution when a voltage is applied in the forward direction of the first embodiment of the light emitting device according to the present invention.

FIG. 4 is a characteristic diagram showing current-light quantity characteristics in a light emitting device according to the present invention.

FIG. 5 is a schematic sectional view illustrating a second embodiment of the light emitting device according to the present invention.

FIG. 6 is a schematic cross-sectional view of a conventional light emitting device.

FIG. 7 is a schematic plan view of a conventional light emitting device.

FIG. 8 is a schematic diagram showing a current distribution when a voltage is applied in the forward direction of a conventional light emitting device.

FIG. 9 is a characteristic diagram showing current-light quantity characteristics in a conventional light emitting device.

[Explanation of symbols]

 1 N-type semiconductor (first conductivity type substrate) 1a N-type semiconductor surface layer part (high phosphorus mixed crystal) 1b N-type semiconductor inner layer part 2 P-type semiconductor (second conductivity type diffusion layer) 2a P-type semiconductor (high phosphorus content) Mixed crystal) 2b P-type semiconductor 3 Positive electrode 4 Negative electrode 5 Selective diffusion film

Claims (1)

[Claims] 1. A first-conductivity-type substrate, and a second-conductivity-type diffusion layer formed on a part of the substrate by impurity diffusion.
In the light-emitting element that applies a forward voltage between the electrodes formed on the surface of the base and the diffusion layer to emit light at the bonding surface of the base and the diffusion layer, the base and the diffusion layer are It is composed of a mixed crystal of ternary or more elements, and the base and the diffusion layer have at least one surface layer portion having a mixed crystal ratio different from that of each main body on the surface portion, at least the surface layer portion A light-emitting device characterized in that a band gap value is set to be larger than a band gap value of each body, and the junction surface for emitting light is deeper than the surface layer portion.