JPS6412114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vertical oscillation type laser using a multilayer structure of hetero semiconductor thin films.

Vertical oscillation lasers emit laser light perpendicular to the substrate, so there is no need to create an optical resonator by cleavage, making it an effective means of integrating semiconductor lasers, increasing output power, and improving reliability. It has been viewed as promising. However, in vertical oscillator lasers, the "thickness" of the active layer determines the effective length of the laser, so the laser gain under the same excitation conditions is a few tenths of that of the conventional structure, making continuous oscillation at room temperature difficult. This was inevitable.

In addition, when creating an actual device, it is difficult to form a mirror on the substrate side. For example, the material used for one active layer is selected on the lower energy bandgap side than the substrate, and the substrate is exposed to laser light. Some methods have been proposed, such as making the substrate transparent and then providing a metal reflective film on the substrate, or etching the two substrates from the back side to expose the lower cladding layer, and then providing a metal reflective film. , the combination of the active layer and the substrate is limited, and the loss of laser light in the substrate cannot be ignored, and the latter requires etching of the substrate, making it difficult to integrate.
The total thickness of the active layer and cladding layer after etching was extremely thin, about 10-odd micrometers, and had the disadvantage of low mechanical strength.

In response to this, attempts have been made to use a hetero-semiconductor multilayer structure as a reflective layer instead of a metal mirror, as seen in Japanese Patent Application Laid-Open No. 56-48192, but consideration has been given to strict phase conditions. In other words, the conditions for the film thickness of important parts were not sufficiently disclosed.
In practice, based only on the fact of the disclosure in the publication,
It has not been possible to provide a vertical oscillation laser that functions satisfactorily.

Under these circumstances, the present invention aims to provide a vertical oscillation type semiconductor laser that has a stable oscillation wavelength, is easy to integrate, and can also obtain high output power. The present invention aims to disclose novel configurations having additional functions and effects unique to each of them.

In FIG. 1 showing the principles and basic embodiments of the present invention, 1 is an upper reflector or wavelength selective mirror made of a multilayer hetero semiconductor thin film, 2 is an active layer where minority carrier injection is performed and becomes a light emitting region; 3 is a lower reflector or wavelength selective mirror having the same structure as the upper reflector, 4 is a substrate that holds the above structure, and 7 is the emission direction of the laser beam.

The basic period of the refractive index change of the upper and lower reflectors is 1/2 of the wavelength of the laser beam in the tube. The fundamental period of the refractive index of 1/2 is the same for the high refractive index medium 5, which has a thickness that is an integral multiple of the 1/4 tube wavelength, and the low refractive index medium 6, which also has a thickness that is an integral multiple of the 1/4 tube wavelength. The reflector can be constructed from a multilayer thin film made up of , or can be obtained by continuously changing the composition in the thickness direction of the reflector with a period of 1/2 the wavelength in the tube.

The thickness of the active layer is set to be an integral multiple of 1/2 the tube wavelength based on the phase condition.

As shown in Figure 1, the active layer may be composed of a homogeneous semiconductor p-n junction that satisfies the above phase conditions, or the active layer itself may have a fundamental period that is an integral multiple of 1/2 wavelength. .

According to the present invention, the refractive index distributions in the reflector and the active layer are considered to be as shown in FIGS. 2a to 2g.
In FIG. 2a, the active layer 2 is composed of a homogeneous semiconductor pn junction with an internal wavelength of n/2, and the reflectors 1 and 3
An example is shown in which a high refractive index medium 5 and a low refractive index medium 6 having a 1/4 tube wavelength are superimposed. Figure 2b
shows an example in which the interferometric reflectors 1 and 3 are constructed by changing the refractive index continuously at a period of 1/2 of the tube wavelength. Figure 2c shows an example in which the active layer 2 also has a refractive index change with a period of 1/2 wavelength, so-called
This is an example of a DFB (distributed feed back) type laser. To satisfy the phase condition of the active layer, the thickness of the central high refractive index medium is 1/2
It is set to the local wavelength.

FIG. 2d shows the case where the upper and lower reflective layers are made of a material with a wider bandgap and lower refractive index than the active layer. This structure reduces absorption of light by the reflective layer and is especially advantageous for laser oscillation in a short wavelength range.

FIG. 2e shows an example in which the number of times the multilayer film of the lower reflective layer is superimposed is greater than the number of times of superimposition of the multilayer film of the upper reflective layer, thereby increasing the reflectance of the lower reflective layer. By increasing the reflectance of the lower reflective layer, it is possible to eliminate emission of the laser light output to the substrate side, thereby increasing the efficiency of the laser.

FIG. 2f shows an example in which a refractive index distribution with a period different from that of the reflective layer is formed in the active layer. In this example, the upper and lower reflective layers are each composed of a periodic structure of a high refractive index medium and a low refractive index medium of 1/4 of the tube wavelength, and the active layer is composed of a semiconductor of 1/2 of the tube wavelength and a 1/4
It is composed of a periodic structure of a low refractive index medium of the tube wavelength. As will be described later, the refractive index distribution with different periods can simultaneously satisfy the wide longitudinal mode gap required for single mode oscillation and the sharp wavelength selectivity of the optical resonator. In this example, the active layer includes, at its center, a semiconductor layer 2' having a thickness of one tube wavelength and also serving as a phase shift plate.

FIG. 2g shows the case where the period of change in the refractive index is varied in the upper and lower reflective layers and the active layer. In this way, with 1/4 pipe wavelength as the basic length,
By freely arranging the active layer medium, the low refractive index reflective layer, and the high refractive index reflective layer, it is possible to construct a vertical oscillation type semiconductor laser having arbitrary optical cavity characteristics.

For the vertical oscillation type laser, two types of current injection methods can be considered, as shown in FIGS. 3a and 3b. Figure 3a shows that when the pn junction is formed parallel to the substrate 4 and perpendicular to the laser beam emission direction 7, b is the pn junction.
A case where the bond is formed perpendicular to the substrate 4 and parallel to the laser beam emission direction 7 is shown. The advantage of structure a is that it is easy to manufacture because a pn junction is formed by simply epitaxially growing the n layer and p layer in sequence, and that the pn junction spreads planarly in the laser emission direction. , the emission area and integrated intensity of the laser beam are strong.

In b, the parasitic resistance of the laser can be reduced because the current does not need to flow through a multilayer reflective layer, and the pn junction is formed along the laser cavity, so the distance over which the laser gain can be obtained is long. It has the following advantages: high efficiency operation with low threshold current can be expected.

However, when comparing the so-called vertical injection type structure shown in FIG. 3a with the lateral injection type shown in FIG. 3b, the lateral injection type is more advantageous.

In the case of the vertical injection type, the laser length is short because it is limited by the diffusion length of minority carriers (2 to 3 μm), and it may be difficult to obtain sufficient gain, whereas in the case of the lateral injection type, In this respect, like edge-emitting lasers (horizontal lasers), the optical resonator and carrier injection directions are perpendicular, so there is no limit in principle to the active layer thickness (laser length), and sufficient gain can be achieved. In other words, it is excellent in that efficient operation can be expected with a low threshold current.

Furthermore, since there is no necessity of sharing the light emitting surface with an electrode, it is possible to avoid the problem that absorption by such an electrode inevitably occurs as in the case of using a vertical injection mechanism. Furthermore, there are other advantages such as the fact that the current does not need to flow across the energy gap of the multilayer reflective layer and the parasitic resistance of the laser can be reduced. A mechanism is preferable.

The vertical oscillation type laser according to the present invention will be described below with reference to GaAs/
A specific example realized using an AlGaAs multilayer heterostructure will be described, and the basic characteristics and application examples will be explained in detail.

Figure 4 shows the configuration shown in Figures 2a and 3a using MBE (molecular beam epitaxy) or MOCVD (metal organic vapor phase).
Here is an example realized using the (deposition) method. In the figure, the same numbers as in FIG. 3 indicate the same parts, 5 indicates the upper p-type electrode, and 6 indicates the lower n-type electrode. The upper and lower parts of the active layer 2 are sandwiched between interference type reflective layers 1 and 3,
An optical cavity is formed perpendicularly to the n ⁺ GaAs substrate 4.

FIG. 5 shows a band diagram of the vertical oscillation laser shown in FIG. 4. Upper and lower interference reflective films 1,
3 are 63 nm GaAs thin films 1 ₁ and 3 ₁ corresponding to 1/4 cavity wavelength of laser light (0.9 μm), respectively.
It has a laminated structure of about several dozen layers including Ga _0.7 and Al _0.3 As layers 1 ₂ and 3 ₂ of 66 nm. The active layer 2 includes a P ^- GaAs layer 2 ₁ and an n ^- GaAs layer 2 each having a thickness of about 3 μm.
Consists of ₂ . By keeping the upper electrode 5 at a potential of about 2V with respect to the lower electrode 6, electron and hole currents are supplied to the central active layer through the p-type and n-type upper and lower reflective layers, respectively, and are recombined. and emit light. Of the emission spectrum, only the wavelength of 0.9 μm is confined by the upper and lower reflective layers 1 and 3, resulting in a laser oscillation state. A portion of the laser light is vertically emitted from a window provided at the center of the upper electrode 5.

In FIG. 5, the upper interference type reflective layer 1 is
Although it is composed of P ⁺ GaAs1 ₁ and P ⁺ GaAlAs1 ₂ , either GaAs1 ₁ or GaAlAs1 ₂ may be non-doped. Similarly, the lower interference type reflective layer 3 is composed of n ⁺ GaAs3 ₁ and n ⁺ GaAlAs3 ₂ , but GaAs3 ₁ or GaAlAs3
Even if any of ₂ is non-doped, conductivity is not hindered. It is also possible to omit the active layer 2 in FIG. 5 and utilize the GaAs layers 1 ₁ and 3 ₁ in the upper and lower reflective layers as light emitting regions as shown in the principle in FIG. 2c.

FIG. 6 shows an example in which the configurations shown in FIGS. 2a and 3b are realized by GaAs/AlGaAs-based heteroepitaxial technology and diffusion technology. In the figure, parts marked with the same reference numerals as in FIG. 4 indicate the same components, and 8 indicates a p-type diffusion region 9 and an n-type diffusion region.

Using continuous heteroepitaxial technology of -V or - compounds, such as GaAs/AlGaAs, all the structures shown in Figures 2 and 3 can be realized by controlling the film thickness during growth. I can do it.

Below, examples of numerical calculations of the various refractive index distributions, film thickness distributions, and number of superimpositions of the reflective layer shown in each figure 2, as well as the loss and wavelength characteristics of the optical resonator are shown, and the realization of this vertical oscillation laser is shown. Explain the characteristics, characteristics, etc.

FIG. 7 shows the steps shown in FIGS. 4, 5 and 6.
The calculation results using the transfer matrix method of the number of superimpositions and reflectance of GaAs/Al _0.3 Ga _0.7 As multilayer reflective layers and the reflection loss at 0.9 μm of an optical resonator sandwiched at both ends by these upper and lower multilayer reflective layers are shown. As mentioned above, the reflective layer consists of a 63nm GaAs layer and a 66nm GaAs layer.
The reflective layer is composed of Al _0.3 Ga _0.7 As layers, and the thickness of the reflective layer increases by 0.13 μm for each superposition. The reflectance is calculated assuming that both ends of the reflective layer are connected to the GaAs layer. Therefore, higher reflection loss is provided than in the case of an actual laser resonator in which the upper reflective layer is in contact with air.

Note that the refractive index used in this calculation is 3.590 for GaAs and 3.385 for Al _0.3 Ga _0.7 As. Further, the loss a of GaAs for 0.9 μm was 26 cm ⁻¹ . Also, assuming that the GaAs layer in the reflective layer is excited, a=0, a=-30 (gain of 30 cm ^-1 )
The case of is also illustrated. AlGaAs at 0.9μm
Layer losses are ignored.

Curve A in Figure 7 represents unexcited GaAs.
This figure shows the relationship between the resonator loss and the number of superimpositions of a multilayer reflective layer of Al _0.3 Ga _0.7 As layers, and corresponds to the configuration shown in FIG. 2a. The resonator loss decreases by one order of magnitude for every 20 layers up to around 70 layers.

The horizontal broken line in the figure indicates the reflectance (0.565) due to the boundary between GaAs and air. As is clear from the position of the intersection with the loss curve, this interference type reflective layer is made of GaAs.
-To indicate the reflectance of the air interface, approximately 10 layers, i.e.
A thickness of 1.3 μm is required. Furthermore, the interference reflection layer having 60 repeated layers exhibits a reflectance of 0.997 and a resonator loss of 0.64×10 ^-2 . The oscillation condition of a semiconductor laser is expressed as a state in which the laser gain in the active layer exceeds the loss in the optical resonator, that is, (ga)·L>ln(1/r ² ). Here, g and a are the laser gain and medium loss per unit length, L is the effective length (thickness) of the active layer, ln (1/r ² ) is the loss of the optical resonator,
r is the electric field reflectance. For example, if a 4 μm thick active layer is excited to such an extent that it has an average gain of 25 cm ⁻¹ , its integral gain will be at the level of 10 ⁻² . This integral gain exceeds the loss level of 0.64×10 ⁻² for an optical cavity with 60 layer repetitions. 25cm
Since an average gain of ^-1 can be achieved at room temperature and at an excitation level of about 3K A/cm ² -μm, the following conclusion can be drawn. In other words, in a vertical oscillation laser that has a structure in which a 4 μm thick active layer is sandwiched between 60 upper and lower (7.7 μm) interference reflective layers,
Continuous oscillation at room temperature is possible by applying an excitation current of 3K A/cm ³ -μm.

Curves B and C in FIG. 7 show the resonator loss when the loss in GaAs is 0 and −30 cm ⁻¹ (gain of 30 cm ⁻¹ ), assuming the configuration of FIG. 2 c.
In the case of curve B in which the GaAs layer is excited and the loss of the medium is canceled out, the optical resonator loss monotonically decreases without being saturated even when the number of repetitions is several tens of layers or more. Curve C shows that the GaAs layer in the reflective layer is 30
The case with a gain of cm ^-1 is shown. Curve C shows that the resonator loss becomes zero when the number of repetitions of the reflective layer is 60.
When a laser gain of 30cm ^-1 occurs in the GaAs part,
It can be seen that laser oscillation is possible. The example described above shows a case where laser gain occurs only in either the uniform active layer or the reflective layer, but the laser gain is generated in both the active layer and the reflective layer (active layer with a periodic structure). It is also possible to share the
As will be described later, it becomes possible to design an optical resonator for the purpose of stabilizing the oscillation spectrum.

When the oscillation wavelength is shortened from 900nm to 875nm,
GaAs losses increase from 26 cm ^-1 to 1000 cm ^-1 .
As a result, when GaAs is used as the high refractive index medium of the reflective layer, the loss of the optical resonator does not fall below 10 ^-1 , as shown by the broken line in FIG. FIG. 8 shows a case where the effect of absorption by the reflective layer is eliminated by using Al _0.1 Ga _0.9 As, which has a larger energy gap than the active layer, as a high refractive index medium used for the reflective layer. Reflective layer is Al _0.1 Ga _0.9 As and Al _0.3 Ga _0.7
When composed of laminated with As, 0.1, 80 in about 50 layers
It shows a resonator loss of 0.01 in the layer. GaAs／
Compared to a reflective layer composed of Al _0.3 Ga _0.7 As, the decrease in resonator loss corresponding to the number of overlaps is small;
The stagnation of resonator loss due to loss in the reflective layer has disappeared. When using a reflective layer composed of Al _0.1 Ga _0.9 As/Al _0.4 Ga _0.6 As, which has a refractive index ratio similar to that of GaAs/Al _0.3 GaAs, the resonator loss curve is approximately the same as that shown in Figure 7B. Similar values were obtained. Furthermore
When using a reflective layer composed of Al _0.1 Ga _0.9 As/Al _0.6 Ga _0.4 As, the resonator loss can be reduced by overlapping about 30 layers.
0.01 is obtained. As shown above, by using a reflective layer with a larger energy gap than the active layer and by increasing the difference in the refractive index ratio, that is, the composition ratio, within the reflective layer, a resonator with low loss can be created. It is important for In the AlGaAs system, when the Al composition exceeds 0.3, the carrier concentration decreases and it becomes difficult to maintain a high transmission rate. In such a case, a third
The method shown in FIG. 3B, in which current is passed only through the active layer, is more advantageous than the method shown in FIG. 3A.

Figure 9 shows the wavelength dependence of the loss and phase of an optical resonator using a multilayer reflective layer composed of 60 layers of GaAs/Al _0.3 Ga _0.7 As. In this example, the film thickness of each layer is set to 1/4 of the internal wavelength of 900 nm, and the optical resonator has a phase shift plate corresponding to 1/2 of the internal wavelength at the center of the optical resonator. The phase difference between the next wave and the second reflected wave becomes zero, resulting in a loss of 0.64×10 ^-2 . However, optical resonator loss ignoring the phase condition has a slight minimum on the long wavelength side because the loss of the medium increases on the short wavelength side. , the black condition of the reflective layer and the phase condition of the optical resonator do not match, so the minimum value is about two orders of magnitude larger than in this example with a phase shift plate. I get used to it. In addition, in this example, the thickness of the active layer constituting the phase shift plate portion is set to 1/2 the tube wavelength, or 0.12 μm, so that the phase rotation, that is, the gap in the longitudinal mode, is reduced.
It has been enlarged to about 20 nm. By increasing the thickness of the active layer, the rotation of the phase with respect to a change in wavelength increases, and a resonance curve whose envelope is the loss curve shown in FIG. 9 is obtained.

In Figure 10 a, b, c, and d, the active layer thicknesses are 1/2λ (0.13 μm), 10/λ (1.3 μm), and 30/λ, respectively.
(3.8 μm) and 100/λ (13 μm), Figure 11 a, b, c, and d are enlarged views of the vicinity of 900 nm of each resonance curve. As is clear from Fig. 10, the resonance point at 900 nm and the gap and peak ratio of the next longitudinal mode become smaller as the active layer becomes thicker.On the other hand, as shown in Fig. 11, as the active layer becomes thicker, Indeed, the resonance curve at 900 nm is sharp. In other words, the longer the active layer is, the more advantageous it is for the longitudinal mode gap and peak ratio, which indicate the stability of the longitudinal mode, but the spectral purity of the laser light or the sharpness of the resonator, which corresponds to noise,
A thicker active layer is more advantageous, and the thickness of the active layer must be selected depending on the purpose. In fact, in the case of Figure 10d, where the active layer thickness is 13 μm, it is 900 nm.
The resonance values at 903 nm are almost equal, and single longitudinal mode oscillation cannot be expected.

On the other hand, as shown in FIG.
The thickness of the active layer is 13μm, whereas the thickness of the active layer is 0.13μm.
The d diagram is about 10 times larger, and the noise bandwidth of the laser beam is also expected to be about 100 times smaller.

The exclusive relationship between longitudinal mode stability and noise characteristics can be resolved by providing refractive index distributions with different periods in the active layer or multilayer reflective layer, as shown in Figure 2 f and g. . Figure 12 a, b
are Al _0.3 Ga _0.7 for each GaAs10/4 tube wavelength, respectively.
A case in which a 1/4 wavelength of As was inserted and a total of 20 layers of refractive index distribution with a period of 0.7 μm were created, 10 layers each on the top and bottom, and a GaAs
The resonance curve is shown when an Al _0.3 Ga _0.7 As 1/4 tube wavelength is inserted for each 5/4 tube wavelength and a refractive index distribution with a period of 0.38 μm is created for a total of 40 layers with 20 layers on the top and bottom. The length of the active layer is 15 μm in figure a and 16 μm in figure b.
Although it is longer than that shown in Fig. 10d, the ratio of the main peak to the sub-peak is 4:1 and 50:1, respectively.
The size is such that single longitudinal mode oscillation is possible. FIGS. 13a and 13b are enlarged views of the vicinity of the peak of the resonance curve in FIG. 12. Figure 13 a, b
It can be seen that has a resonator Q of the same order as that in FIG. 11d.

As shown above, the vertical oscillation laser according to the present invention can improve the oscillation wavelength, longitudinal mode stability, noise characteristics, and output by optimizing the period and number of superimpositions of the refractive index distribution according to each specification. etc. can be set freely.

Above, with 1/4 tube wavelength as the fundamental period,
Although the explanation has been given using a GaAs/AlGaAs multilayer film, the present invention can be applied to any system in which continuous heteroepitaxy is possible and lattice matching can be achieved. Applicable examples include zinc chalcogenide systems on GaAs substrates for the - group, and GaInAsP, GaAlInp, and GaAlInp systems for the - group.
Examples include GaAlSb.

In addition, the above discussion assumed a homogeneous refractive index distribution in the 1/4 tube wavelength, that is, in the range of several tens of nanometers, but if the refractive index distribution with the fundamental period of 1/4 tube wavelength is By adding an energy gap period of about 10 Å, the conventional argument holds true for light, and for carriers, a structure in which quantum effects occur can also be considered. FIG. 14 shows an example in which the high refractive index medium and active layer of the upper and lower reflectors are formed of GaAs of 60 Å and a superlattice of AlGaAs. Electrons and holes are confined in quantum wells 10 with a width of 60 Å and are quantized, while laser light is transmitted through the average refractive index n _W of the GaAs/AlGaAs superlattice and the large energy gap of the reflective layer. Sensing the difference between the refractive index n and _C , it undergoes diffraction.

In general, by changing the density per unit volume of the quantum well distribution, a low energy gap region of several tens of angstroms wide, which is necessary to form a quantum well, can be created.
It is possible to simultaneously form a refractive index distribution with a period of several tens of nanometers, and because it has quantum wells,
It is possible to obtain a vertical oscillation type semiconductor laser which has advantages such as having a small temperature dependence of threshold current and being able to emit light with higher energy than that of the host crystal.

10 to 13, depending on the thickness and refractive index distribution of the active layer. Although differences in resonance curves were shown, this difference is thought to be mainly due to changes in phase rotation in the active layer. Therefore, by further providing a phase shifter capable of external modulation inside the active layer or adjacent to the active layer, it becomes possible to change the oscillation conditions from the outside. Figure 15 a, b
shows an example in which a phase shifter using a pn junction depletion layer is provided adjacent to the active layer.

Figure 15a shows the GaAs/
pn forming the active layer of GaAlAs vertical oscillation laser
A vertical oscillation laser with a modulator is shown superimposed on the junction 2 and formed of an np junction 11 parallel to the substrate and an electrode 12 for applying a reverse bias to this np junction through the upper reflective layer 1. In this laser, a forward current is passed through the upper electrode 5 and the lower electrode 6 to keep the active layer 2 in an excited state, and then a reverse bias is applied to the modulation electrode 14 and the upper electrode 5, whereby the phase due to carrier depletion is Phase matching is performed using changes in conditions. Figure 15b
shows a vertical oscillation laser with a modulator based on the structure of the vertical oscillation laser shown in FIG. A GaAlAs insulating layer 16 and an upper reflective layer 1 are formed to overlap the active layer 2 in FIG. By maintaining a reverse bias state using the electrode 12 and the p-type electrode 13, the refractive index of the upper reflective layer can be changed. Since the change in the refractive index of the upper reflective layer changes the optical distance of the multilayer reflective layer, it is possible to change the wavelength at which the multilayer reflective layer exhibits the maximum reflectance.

In other words, when using a phase shifter using an np junction,
Simultaneously with amplitude modulation, frequency modulation of laser light becomes possible.

Semiconductor lasers can be externally modulated by forward energization, but if a phase shifter using a pn junction or the like is used, 1. There is no need to control the large current required for minority carrier excitation, so high-speed modulation is possible. is easy. In fact, phase shifters that utilize the Karr effect or depletion effect appear electrically capacitive, so they require almost no power to change the oscillation conditions.

2. Since the spatial distribution of minority carriers is not changed with modulation, there is less modulation delay and distortion of the modulated waveform due to re-spreading of minority carriers.

3. By changing the phase condition, it becomes possible to modulate the frequency of the semiconductor laser, which was impossible with modulation by forward energization.

In particular, in structures such as the vertical oscillation laser provided by the present invention, which has a shorter cavity length and a wider spacing between adjacent longitudinal modes than conventional edge-emitting (horizontal) lasers, A phase modulation method with such effects is extremely advantageous.

FIG. 16 shows upper and lower electrodes 5a to 5, respectively, of the vertical oscillation type laser shown in FIG.
This shows the case where the image is divided into four parts, 5d, 6a to 6d.
For example, when a bias voltage is applied between the upper electrodes 5a and 5b and the lower electrode 6b, the current flowing through the upper and lower conductive reflective layers and the active layer will flow from the vertical direction as shown by streamline A in the figure. Lean. Therefore, in the upper part of the active layer, the excitation on the right side is stronger, and in the lower part, the excitation on the left side is stronger, so that the output of the laser light is slightly tilted. Furthermore, if it is desired to emit laser light vertically, it is sufficient to pass current through all four sets of electrodes.

By appropriately selecting the pair of upper and lower electrodes while appropriately correcting the oscillation threshold depending on the laser emission angle, it is possible to deflect the laser beam to any angle with the structure shown in Figure 16. It becomes possible.

FIG. 17 shows that using the vertical oscillation laser,
This is an example in which a laser matrix was created on a GaAs semi-insulating substrate. The laser matrix of this example includes a laser body 2, 3, 4 consisting of an upper electrode 1, reflective layers 2, 4, and an active layer 8, an n ⁺ conductive layer 17, an insulating film 18 for element isolation, and a GaAs semi-insulating substrate 19.
It is composed of. By selecting a combination of the upper electrode 1 and the n ⁺ conductive layer 17, the laser bodies 2, 3, and 4 can be energized in the forward direction at the location where the upper electrode 1 and the n ⁺ conductive layer 17 intersect. Therefore, by sequentially holding the upper electrode 1 at ground potential while applying a negative voltage to any number of n ⁺ conductive layers 17, the light emitting pattern of the laser array in the horizontal direction can be sequentially swept vertically while changing the light emission pattern. I can do it. This example is an example in which an 8×8 matrix is formed, but by using an appropriate driving device, for example,
Can be used as a character generator. Further, by using a 1024-column linear laser array to construct a high-speed line printer or a 256×256 laser array, an image pattern generator or a three-dimensional hologram generator can be constructed.

As described above, the present invention provides a fully practical vertical oscillation semiconductor laser using a hetero-semiconductor multilayer film by disclosing the phase matching conditions. The laser length can be secured, and the oscillation threshold current characteristics and spectrum characteristics can also be greatly improved. Furthermore, it also makes it possible to realize an ultrahigh-speed modulation laser that incorporates a modulator within an optical resonator.

Therefore, in the end, the present invention has improved output, lifetime, and oscillation wavelength stability compared to Fabry-Perot or Bratz reflector semiconductor lasers that have been put to practical use as edge-emitting or horizontal semiconductor lasers. It is superior in almost all aspects such as performance, ease of integration, and manufacturing yield, and is suitable for all fields in which semiconductors will expand in the future, such as optical communications, video disks, laser printers, image pattern generators, It is thought that the conventional structure will be replaced with power laser light memory and the like.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the vertical oscillation type laser of the present invention, Fig. 2 is a diagram of various refractive indexes and band diagrams of the vertical oscillation type laser, Fig. 3 is a schematic diagram of the configuration of different current injection structures, and Fig. 4 5 is a band diagram of an embodiment of the configuration shown in FIG. Schematic configuration diagram, Figures 7 and 8 are explanatory diagrams of the number of overlaps of the reflector and resonator loss of the embodiment according to the configuration shown in Figures 4 to 6, Figure 9 is an explanatory diagram of oscillation wavelength versus resonator loss, and Figure 10 is an explanatory diagram of the resonator loss versus oscillation wavelength. Resonance curve diagrams for each example, Figure 11 is the wavelength in Figure 10
An enlarged explanatory diagram around 900 nm, Fig. 12 is a resonance curve diagram of another example, Fig. 13 is an enlarged explanatory diagram of the vicinity of the peak in Fig. 12, and Fig. 14 is an explanatory diagram of the refractive index of an example with quantum wells. An explanatory diagram of the band, FIG. 15 is a schematic diagram of an embodiment having a phase shifter, FIG. 16 is a schematic diagram of an embodiment having a laser beam deflection ability, and FIG.
The figure is a schematic configuration diagram of an application example in which a laser matrix is assembled using the laser of the present invention. In the figure, 1 is an upper reflector, 2 is an active layer, 3 is a lower reflector, 4 is a substrate, 5 is a high refractive index medium constituting the reflector, 6 is a low refractive index medium, 7 is a laser beam or its emission direction, 8 is a p-type diffusion region,
9 is an n-type diffusion region, 10 is a quantum well, 11 is a pn junction for a phase shifter, 12 is an electrode for a modulator, 13 is a p-type electrode for a modulator, 14 is an n-type diffusion layer, 15 is a p-type diffusion layer, 16 is a AlGaAs insulating layer, 17 is n ⁺ conductive layer,
18 is an isolation insulating film, and 19 is a GaAs semi-insulating substrate.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate has a lower reflector, an active layer, and an upper reflector that are continuously formed in the vertical direction with respect to the main surface of the substrate, and the lower and upper reflectors are configured to absorb laser light. consisting of a multilayer structure of hetero semiconductor thin films having a film thickness that is an integral multiple of 1/4 of the wavelength within the medium of the active layer, and the thickness of the active layer is an integral multiple of 1/2 of the wavelength within the medium of the laser beam. A vertical oscillation type semiconductor laser featuring: 2. The vertical oscillation semiconductor laser according to claim 1, wherein the fundamental period of the refractive index of the active layer changes within the same laser resonator. 3. The vertical oscillation type semiconductor laser according to claim 1, wherein the distribution period of the refractive index in the thickness direction in the multilayer structure of the hetero semiconductor thin film changes within the same laser resonator. 4. Claim 1, characterized in that the active layer has a refractive index distribution with a basic period of 1/4 internal wavelength, and includes therein a phase shift plate having a thickness that is an integral multiple of 1/2 internal wavelength. The vertical oscillation semiconductor laser described above. 5. The vertical oscillation type semiconductor laser according to claim 1, wherein the fundamental period of the refractive index of the upper and lower reflectors and the fundamental period of the refractive index of the active layer change within the same laser resonator. 6 The active layer is composed of p-type and n-type semiconductors placed side by side on the left and right, and the pn junction in the active layer composed of them extends parallel to the laser beam and perpendicular to the substrate. , wherein the carrier injection into the active layer via the pn junction is performed in a lateral direction parallel to the substrate. laser. 7 At least a part of the multilayer structure of the hetero semiconductor thin film is made of the same semiconductor material as the active layer, and by injecting minority carriers also into this same semiconductor material part, the multilayer structure forming the reflective layer is 7. The vertical oscillation type semiconductor laser according to claim 1, wherein the vertical oscillation type semiconductor laser has a gain. 8. Any one of claims 1 to 7, characterized in that an electrically controllable phase shifter is installed in a portion adjacent to the active layer inside the laser resonator and has a high-speed modulation function. The vertical oscillation semiconductor laser described in . 9. The vertical oscillation type semiconductor laser according to claim 8, characterized in that a depletion layer generated under reverse bias conditions of a semiconductor pn junction is used as a phase shifter. 10. The vertical oscillation semiconductor laser according to claim 8 or 9, wherein the phase shifters are provided in a matrix in a portion adjacent to the active layer.