JP2685788B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a semiconductor light emitting device that oscillates in a visible light region.

(Prior Art) (Al _x Ga _1-x ) _0.5 In _0.5 P-based material is lattice-matched with a high-quality GaAs substrate, and by changing the composition of Al and Ga,
That is, by changing the value of X from 0 to 1, the band gap can be changed in the range of about 1.8 eV to about 2.35 eV. The oscillation wavelength is about 0.68 μm to about 0.
This corresponds to 56 μm. While the wavelength can be freely changed in this way, the active layer is X = 0, that is, Ga _0.5 In _0.5 P
The structure in which the cladding layer is (Al _x Ga _1-x ) _0.5 In _0.5 P has recently become the mainstream. Usually, in order to oscillate the semiconductor laser at a low threshold and at a high temperature, it is necessary to make the band gap difference ΔEg between the active layer and the cladding layer as large as possible. Generally, ΔEg is required to be 0.3 eV or more. Therefore, the value of Al composition X of the cladding layer is selected from 0.4 to 0.5. However, when the photoluminescence peak wavelength at room temperature (25 ° C.) was measured while changing the Al composition X, it became as shown in FIG. The horizontal axis represents Al composition X and the vertical axis represents wavelength. It was found that when X <0.7, it can be expressed by an equation of approximately λ = −172X + 662 (nm). From this figure, the band gap difference ΔEg between the active layer and the clad layer is calculated, and when X = 0.4, ΔEg
= 0.215eV and X = 0.5, ΔEg = 0.28eV. These values are considered to be insufficient for low threshold oscillation of the semiconductor laser. When a full-face electrode type semiconductor laser was actually prototyped, the oscillation threshold current density at X = 0.4 was extremely high at ³ kA / cm ^2, and even when X = 0.5.
It was relatively large at 1.6 to ² kA / cm ² . Further, the characteristic temperature T ₀ was also small, and high temperature oscillation could not be obtained.

(Problems to be Solved by the Invention) As described above, the conventional dalb heterostructure (X = 0.4 to
0.5), the band gap difference ΔEg between the clad layer and the active layer is ΔEg
It was difficult to raise the voltage to 0.3eV or more, and the oscillation threshold current density was large.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a semiconductor light emitting device that can operate at high temperature with a low threshold value.

[Structure of the Invention] (Means for Solving the Problems) This invention relates to semiconductor light emission having a double hetero structure in which GaInP is an active layer and (Al _x Ga _1-x ) _y In _1-y P is a P clad layer. In the device, the Al composition X of the P-clad layer is 0.65 to
The feature is that it is 0.75.

(Operation) According to the present invention, the Al composition X of the cladding layer is 0.65 to 0.
Since it is set to 75, ΔEg can be made large, the characteristic temperature T ₀ of the semiconductor laser can be increased, and a low threshold and high temperature operation can be realized.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples. FIG. 1A is a sectional view showing a first embodiment of the present invention. n-GaAs buffer layer 10 on n-GaAs substrate 101
2, n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first cladding layer 103 having a thickness of 0.6 μm, Ga _0.5 In _0.5 P active layer 104 having a thickness of 0.1 μm,
P- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 105 having a thickness of 0.6 μm, p-In _0.5 Ga _0.5 P intermediate bandgap layer 112
In this structure, the n-GaAs current confinement layer 106 having a thickness of 1 μm and the p-GaAs contact layer 107 having a thickness of 3 μm for forming ohmic contact are formed. On the p-GaAs contact layer 107, P-type electrodes AuZn108 and n-GaA are formed.
AuGe109, which is an N-type electrode, is formed on the surface of the substrate 101. When a current is injected into the device of this example, n-Ga
The injection current is limited to the current confinement portion 110 due to the pn inversion layer formed by the As current confinement layer 106. Therefore, light emission occurs in the active layer 4 substantially along the current constriction portion 110, and laser oscillation is also obtained.

Here, FIG. 2 shows the relationship between the energization time and the operating current in an energization test of 40 ° C. and 3 mW when the carrier concentration of the n-clad layer is changed in the semiconductor laser according to the present embodiment.
The carrier concentration of the p-cladding layer was 2 × 10 ¹⁷ cm ⁻³ , the carrier concentration of the active layer was 1 × 10 ¹⁶ or less, the stripe width of the laser was 7 μm, and the resonator length was 300 μm. As a result, when the carrier concentration of the n-cladding layer exceeded 5 × 10 ¹⁷ cm ⁻³ , the operating current rapidly increased due to the initial energization, and stable continuous oscillation became impossible. However, if the carrier concentration of the n-cladding layer is less than 5 × 10 ¹⁷ cm ^-3 , the operating current is stable at about 90 mA, and these semiconductor lasers operate stably for 1000 hours or more. Therefore, n
If Si is used as the impurity on the cladding layer side and the carrier concentration is less than 5 × 10 ¹⁷ cm ⁻³ , a highly reliable semiconductor laser with a low threshold value can be obtained.

Then, P-InGaAlP to indicate the optimum range of the Al composition of the clad layers, the clad layer _{P- (Al x Ga 1-x} ) y In 1-y P,
(0 <X <1,0 <y <1), and this Al composition X
The optimum range of will be described.

For the composition y of (Al _x Ga _1-x ), (Al _x Ga _1-x ) on the GaAs substrate
_x Ga _1-x ) _y In _1-y P in order to form a lattice match,
y needs to be 0.5, but may be in the range of 0.45 to 0.55.

In FIG. 3, the horizontal axis is A | composition X, the vertical axis is the oscillation threshold current density J _th of the semiconductor laser shown in FIG. 1 on the left, and the characteristic temperature T ₀ and the maximum oscillation temperature ^cw _max are on the right. Was taken,
Experimental values are shown. The maximum oscillation temperature Tmax is one of the characteristics of the semiconductor laser, and the quality of the semiconductor laser can be determined by how large it can be. This Tm
ax and other laser parameters characteristic temperature T ₀ , series resistance
Rs, thermal resistance Rth, and pulse oscillation threshold value I _th ^p have the following relationship.

I _th ^p = I ₀ exp (T / To) I _th ^cw = I ₀ exp [(T + ΔT) / T ₀ ] ΔT = (Vj + I _th ^cw Rs) I _th ^cw R ^th where I ₀ is oscillation at 0 ° C. Threshold, T is the heat sink temperature, ΔT is the temperature rise in the active region, Vj is the junction voltage, and I _th ^cw is the continuous oscillation threshold. From the above formula, Tmax
Figure 4 shows the relationship between the and parameters. The horizontal axis shows T ₀ and the vertical axis shows T max, and I _th ^p is shown as a parameter. As can be seen, the more Tmax if large T ₀ increases. If I _th ^p becomes smaller, Tm
ax becomes large. This T ₀ largely depends on the impurity carrier concentration of the p-cladding layer. FIG. 5 shows the relationship between the experimentally determined T ₀ and the p carrier concentration. It can be seen that T ₀ increases as the p-carrier concentration increases.

First, paying attention to Jth in FIG. 3, when X = 0.4, about 3 kA /
large and cm ^2, X = 0.5, even it can be seen that relatively large 1.8kA / cm ^2. However, when X = 0.7, it can be reduced to 1.3 kA / cm ² , and X = 0.7 is extremely superior to X = 0.4 to 0.5. Further, it can be seen that T ₀ increases as the value of X increases for the characteristic temperature T ₀ . For example, when X changes from 0.5 to 0.7, T ₀ changes from 70K to 85K, and Tmax increases by about 20 ° C.

Here, the optimum range of the Al composition X will be described. First,
As a P-type dopant for the P-type cladding layer, there is Mg,
It is difficult to control the PN junction formation with this Mg. Therefore,
Zn, which has good controllability, is used as the P-type dopant. In the case of this Zn, when the Al composition X is X = 0.8, the P-carrier concentration can be realized only up to 1 × 10 ¹⁷ (cm ⁻³ ), T ₀ decreases and the maximum oscillation temperature decreases. According to the experiments by the present inventors, when X = 0.75, the P-carrier concentration is 2 × 10 ¹⁷ (cm ⁻³ ).
It was confirmed that T ₀ can be made as good as 90K.

Also, with this InGaAlP-based semiconductor laser, 50 (° C)
It was found that when T _max ^cw is less than 70 (° C), it is difficult to make the laser oscillation stable in the new generation hand test. This T _max ^cw is less than 70 (° C)
As can be seen from FIG. 3, X is less than 0.6. Therefore, P
The Al composition X of-(Al _x Ga _1-x ) _y In _1-y P may be in the range of 0.65 to 0.75. In addition, when the range of this Al composition is converted into the photoluminescence peak wavelength at 25 ° C, it is changed from 530 nm to 5
It becomes 50 nm.

Next, the optimum range of the P-carrier concentration of this P-clad layer will be shown. First, the carrier concentration of the n-clad layer is 5 × 10 ¹⁷ (c
It must be less than m ^-3 ). If Zn is used as the P-type dopant of the P-clad layer at this time, the P-carrier concentration is 5 × 10 5 to prevent Zn from diffusing from the P-clad layer to the n-clad layer through the active layer. ^It was confirmed experimentally that it should be less than ¹⁷ . That is, the sixth
As shown in the figure, when X is changed to X = 0.5, 0.6, and 0.7, when the P-carrier concentration exceeds 5 × 10 ¹⁷ (cm ^-3 ), the oscillation threshold is caused by Zn diffusion. Rises sharply. When the P-carrier concentration becomes smaller than 2 × 10 ¹⁷ (cm ^-3 ), the electric resistance becomes high, the heat generation of the semiconductor laser occurs, and the oscillation threshold value increases from about 70 mA to about 80 mA,
Moreover, there is a problem that T ₀ becomes small. Therefore, P- (Al _x Ga
_The P-carrier concentration of _1-x ) _y In _1-y P may be in the range of 2 × 10 ¹⁷ (cm ⁻³ ) to 5 × 10 ¹⁷ (cm ⁻³ ).

The optimum ranges of the Al composition and the P-carrier concentration of the P- (Al _x Ga _1-x ) _y In _1-y P cladding layer have been shown above, but the n-type (Al _x Ga _1-x ) _y In _{1 Also in the -y} P clad layer, it is desirable to set the Al composition X in the range of 0.65 to 0.75 for the same reason. However, the degree of influence of carriers as a semiconductor laser on leakage is greater in the P-type cladding layer than in the n-type cladding layer. Therefore, it is more effective to set the Al composition of the P-type cladding layer in the above range.

Furthermore, the present invention is applied not only to the semiconductor laser shown in FIG. 1 but also to the semiconductor laser as shown in FIG. As shown in FIG. 7, n-GaAs substrate 211
The Si-doped n-GaAs buffer layer 212, n- (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P clad layer 213, Ga _0.5 In _0.5 P active layer 21
4, P- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 218 is formed in a mesa type, n-GaAs current blocking layers 217 are selectively grown on both sides of this, and finally a P-GaAs contact layer is grown on the entire surface. It has a structure. The feature of this structure is P- (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P The thickness of the clad layer 215 is reduced to about 0.3 μm, and the transverse mode is controlled by absorption in the n-GaAs current blocking layer. Therefore, a stable fundamental transverse mode oscillation can be obtained at a low threshold value.
Further, since the P-Ga _0.5 In _0.5 P etching stop layer 216 is present, the controllability of etching is also very excellent.
In this case, the P-cladding layer 215 forms the cladding layer P
-(Al _x Ga _1-x ) _y In _1-y P, Al composition X is 0.65 to 0.7
It should be within the range of 5. The P-carrier concentration is 2 to
It should be in the range of 5 × 10 ¹⁷ .

[Advantages of the Invention] As described above, according to the present invention, a semiconductor laser having a low threshold and capable of operating at high temperature can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a semiconductor laser to which the present invention is applied, FIG. 2 is a diagram showing carrier concentration characteristics of an n-type cladding layer, and FIG. 3 is an oscillation with Al composition X of a P-type cladding layer. Threshold current density J _{th'Characteristic} temperature T ₀ and maximum oscillation temperature T ^cw _max are shown in FIG. 4, FIG. 4 is a diagram showing the relationship between T ₀ and ▲ T ^CW _max ▼, and FIG. 5 is P-carrier concentration And a diagram showing the characteristic temperature T ₀ ,
FIG. 6 is a diagram showing the relationship between the P-carrier concentration and the oscillation threshold value, FIG. 7 is a diagram showing an example of another semiconductor laser to which the present invention can be applied, and FIG. 8 is an Al composition X and photoluminescence peak wavelength. It is a figure which shows the relationship with. 108 ... AuZn electrode 107 ... P-GaAs 106 ... n-GaAs 112 ... P-In _0.5 Ga _0.5 P cap layer 105 ... P-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P 104 ... Undoped In _0.5 Ga _0.5 P active layer 103 …… n-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P 102 …… n-GaAs 101 …… n-GaAs substrate 109 …… AuGe electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 63-285991 (JP, A) JP 1-145882 (JP, A) JP 1-243482 (JP, A)

Claims (2)

(57) [Claims] 1. An active layer of GaInP, comprising at least (Al _x Ga
_1-x ) _y In _1-y P is a semiconductor light emitting device having a double heterostructure in which P-type and N-type cladding layers are used, and the Al composition X of the P-type cladding layer is within the range of 0.65 to 0.75 and the semiconductor light-emitting device of the impurity carrier concentration of 5 × 10 ¹⁷ cm ^-3, characterized in that the said N-type cladding layer less than 5 × 10 ¹⁷ cm ^-3 impurity carrier concentration of. 2. The semiconductor light emitting device according to claim 1, wherein the photoluminescence peak wavelength of the P-type cladding layer at 25 ° C. is 530 nm to 550 nm.