KR20080076784A - Red surface emitting laser element, image forming device, and image display apparatus - Google Patents

Abstract

A red surface light emitting laser element, an image forming device and an image display device are provided to improve a high temperature operation characteristic by increasing the thickness of a p-type spacer layer. A red surface light emitting laser element includes a first reflective mirror(302), a second reflective mirror(308), an active layer(305), and a p-type semiconductor spacer layer(307). The second reflective mirror has a p-type semiconductor multi-layer. The active layer is installed between the first reflective mirror and the second reflective mirror. The p-type semiconductor spacer layer is installed between the active layer and the second reflective mirror and has a thickness ranging from 100nm to 350nm. The p-type semiconductor spacer layer has aluminum, indium and phosphorus.

Description

RED SURFACE EMITTING LASER ELEMENT, IMAGE FORMING DEVICE, AND IMAGE DISPLAY APPARATUS}

The present invention relates to a red surface emitting laser element, and an image forming apparatus and an image display apparatus incorporating the red surface emitting laser element.

A. Usefulness of Red Surface Emitting Laser Devices

Surface-emitting laser elements (especially vertical cavity-type surface-emitting lasers (VCSELs) are used to output light in a direction perpendicular to the surface direction of a semiconductor substrate). At the same time, it can be formed relatively easily as a two-dimensional array.

When the device is formed as a two-dimensional array, since parallel processing is realized by the multi-beams emitted therefrom, applications for various industrial uses of this two-dimensional array technology are desired to achieve high density and high speed.

For example, if a surface emitting laser array can be used as an exposure light source of an electrophotographic printer, the printing speed can be increased by parallel processing of the printing process by the multi-beams.

BACKGROUND OF THE INVENTION A surface-emitting laser that is currently in practical use is an element that outputs laser light in an infrared region (wavelength lambda = 0.75 µm to 1 µm). If the oscillation wavelength is shorter, the beam diameter can be further reduced, and a higher resolution image can be obtained.

The red surface emitting laser outputs light of a wavelength shorter than the infrared region (about 0.6 mu m to about 0.73 mu m). In addition, at this wavelength, the sensitivity of amorphous silicon that can be applied to the photosensitive drum of an electrophotographic printer is very high.

Therefore, in order to achieve high-speed, high-resolution image printing using a photosensitive drum made of amorphous silicon, the practical use of a red surface emitting laser is now desired.

In addition, the effect due to the combination of high resolution and multi-beam parallel processing by such a short wavelength is very large. This combination is expected to contribute to various fields including electrophotographic printers and image display devices such as laser displays.

B. Basic Configuration of Red Surface Emitting Laser

In order to generate light having a wavelength in the red region, AlGaInP, which is a semiconductor material, is typically used. The lattice of this material matches the lattice of GaAs, the material constituting the deposition substrate, and its bandgap energy can be controlled by varying the composition ratio of aluminum and gallium.

In order to cause laser oscillation, it is necessary to inject a threshold current or more into the laser element. Due to the injection of electric current, carriers such as electrons or holes can be injected into the active layer, which is eventually converted into light upon radiative recombination.

C. Of Prior Art Embodiment

The red surface emitting laser is formed by inserting a resonator region including an AlGaInP active layer between the multilayer film reflectors made of AlGaAs, which is another semiconductor material. As the substrate, a GaAs substrate is lattice matched with the lattice of the active layer and the multilayer film reflector, respectively.

In 1995, a group led by Crawford of the Sandia National Laboratory, published a device configuration of a one-wavelength resonator structure (MH Crawford et al., IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 7, No. 7). 1995), 724, hereinafter referred to as the Crawford literature.

This one-wavelength resonator structure has a resonator length which is most widely used in surface emitting lasers that output infrared light. In the red surface emitting laser, the length of one wavelength resonator is about 200 nm (when the wavelength is 680 nm) in terms of layer thickness.

In particular, an active layer having a multi-quantum well structure of 40 nm to 50 nm thick is disposed in the central region of one wavelength resonator length. On both sides of the active layer, a p-type AlGaInP layer and an n-type AlGaInP layer each having a thickness of 80 nm or less are disposed as a spacer layer.

In some cases, an undoped spacer layer is disposed between the active layer and the doped p-type (or n-type) spacer layer. In this case, the thickness of the p-type (or n-type) AlGaInP spacer layer is about 50 nm.

In the Crawford literature, the thickness of the p-type or n-type AlGaInP layer is about 50 nm.

The Crawford literature also teaches that the maximum luminous intensity in the 675 nm mode is 2.8 mW (20 ° C.) from devices with 15 μm phi oxide openings.

When using a red surface emitting laser element as a light source for electrophotography, high operating characteristics at high temperature are required.

However, the Crawford document discloses that, according to its element configuration, when the environmental temperature rises from 20 ° C to 40 ° C, the maximum luminescence intensity is significantly reduced. In particular, in the 675 nm mode, its maximum luminous intensity is reduced to about 1.0 mW (output drop to less than 40%).

Further, the present inventors found that even if the environmental temperature is 20 ° C, when the current injection amount is increased for the purpose of increasing the output operation, the internal temperature of the element increases to 20 ° C or more as the current injection amount is increased. In this case, the light emission intensity may not increase or decrease with increasing current injection amount, so that the maximum light emission intensity is limited.

This decrease in luminescence intensity is believed to occur because leakage current that does not contribute to luminescence increases considerably with temperature rise.

Therefore, there is a need for a novel red surface emitting laser element capable of reducing the amount of leakage current, and an image forming apparatus or image display apparatus incorporating such a red surface emitting laser element.

A first aspect of the invention is a first reflector; a second reflector including a p-type semiconductor multilayer film; An active layer between the first reflecting mirror and the second reflecting mirror; And a p-type semiconductor spacer layer between the active layer and the second reflecting mirror and having a thickness of 100 nm or more and 350 nm or less.

The second aspect of the invention is a first reflecting mirror; a second reflecting mirror comprising a p-type AlGaAs semiconductor multilayer film; An active layer between the first reflecting mirror and the second reflecting mirror; And a p-type AlInP semiconductor spacer layer or a p-type AlGaInP semiconductor spacer layer having a thickness of 100 nm or more and 350 nm or less between the active layer and the second reflecting mirror.

A third aspect of the invention the first reflecting mirror; a second reflector including a p-type semiconductor multilayer film; An active layer between the first reflecting mirror and the second reflecting mirror; And a p-type semiconductor spacer layer between the active layer and the second reflector. In this red surface emitting laser element, the conduction band edge at the point of the p-type semiconductor multilayer film is lower than the conduction band end at the point of the p-type semiconductor spacer layer, and the p-type semiconductor spacer layer The thickness of is 100 nm or more and 350 nm or less.

In addition, an image forming apparatus and an image display apparatus are also provided. Each of these includes a red surface emitting laser element as described above and a deflector for scanning by deflecting the laser light output from the laser element.

According to the present invention, there is provided a novel red surface emitting laser element having a reduced amount of leakage current, and an image forming apparatus and an image display apparatus including such a red surface emitting laser element.

Further features of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings.

As described above, in the red surface emitting laser element having the structure described in Crawford's literature, the operating characteristics at high temperatures are significantly deteriorated.

The present inventors have assumed that the cause is that the leakage current amount increases sharply due to heat, and that the sudden increase in the leakage current amount causes a significant drop in luminous efficiency.

FIG. 6 is a paper on red VCSEL as in Crawford literature [R. P. Schneider et al., IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 6, No. 3 (1994) 313 (hereinafter referred to as "Schneider Literature").

In particular, Figure 6 is an active layer, AlInP spacer layers (the spacer layers are sometimes also denoted as "cladding layer") and composed of semiconductor multilayer film that functions as a reflector DBR (distributed Bragg reflector) region (AlAs / Al _{0 .5} Ga _.5 shows the band diagram of the multi-layer film As). DBR is used as a reflector of a resonator.

FIG. 6 shows that the end of the conduction band (CB side of FIG. 6) of the component of the DBR region is higher than the band end of AlInP constituting the spacer layer.

That is, this diagram shows that electrons overflowing the hetero barrier between the active layer and the AlInP spacer layer are difficult to diffuse beyond the thickness of the AlInP layer.

On the other hand, the element structure disclosed in the Crawford reference, the reflector comprising a multilayer film including an active layer, p-type Al _{0 .25} Ga ₀ adjacent to the active layer In _{0 .25 .5} P spacer layer, and 34 pairs of layers, each pair is a p-type AlAs layer about 50 ㎚ thickness of about 50 and p-type Al ㎚ thickness _{0 .5 0 .5} includes a Ga as layer.

In this case, the thickness of the p-type layer which is the sum of the thicknesses of the p-type AlInP spacer layer and the p-type DBR layer is 3 µm or more.

As described above, when the p-type DBR region having a higher conduction band end than the p-type spacer layer is sufficiently thick, the probability that electrons injected from the n-type semiconductor layer into the active layer overflows the p-type spacer layer adjacent to the active layer and becomes a leakage current. Can be extremely small.

This means that in the spacer layer, the concentration gradient of electrons overflowing from the active layer becomes more gentle than when no p-type DBR region is provided.

The magnitude of the diffusion current related to leakage depends on the electron concentration gradient. Thus, the band diagram shown in FIG. 6 shows that the amount of diffusion current component of the leakage current generated by the electrons beyond the spacer layer needs to be quite small.

However, as described above, the red surface emitting laser device has poor temperature characteristics.

In the red surface emitting laser element, the resonator region inserted between the upper and lower multilayer film reflectors is usually made of AlGaInP, while the multilayer film reflector is usually made of AlGaAs. That is, the resonator region is made of a material different from that of the multilayer film reflector region.

In the red surface emitting laser device, both the p-type semiconductor spacer layer (for example, p-type AlGaInP spacer layer) and the p-type DBR region (for example, AlGaAs layer) are provided as the p-type layer. This unique structure is not found in infrared surface emitting lasers in which all layers are made of AlGaAs-based materials.

That is, in order to analyze the influence on the leakage current in a device including a multilayer structure composed of different materials having the same conductivity type, it is necessary to analyze in detail the position of the end of the conduction band, which is the potential at which electrons are affected.

Therefore, the potential of electrons is examined by simultaneously considering the following two factors for the p-type spacer layer and the constituent layer of the p-type DBR region of the red surface emitting laser device:

[1] Since these p-type layers are doped with p-type impurities, the Fermi level of each layer is located approximately at the band end of the valence band;

[2] p-type Al _x Ga ₁ is used as the semiconductor spacer layer _{- x In 0 .5 P (0.25≤x≤0.55} , especially 0.35≤x≤0.5-in area), and, Al _y Ga ₁ constituting the DBR _{region, y} As (0.4 ≦ _y ≦ 1) is not a direct transition type semiconductor but an indirect transition type semiconductor, and the band end portion of the conduction band is not a Γ point but an X point. However, the Γ point is an area where the bottom of the conduction band end is considered to lie directly in the transition type semiconductor.

Based on the two points [1] and [2], the band end lineup at the potential of the electron, that is, the X point in the conduction band, is shown as the solid line 1010 shown in FIG. In Fig. 1, the horizontal axis represents the thickness of the device, and the vertical axis represents the band offset amount with respect to GaAs. The positive side region is the conduction band side, and the negative side region is the valence band side.

In Fig. 1, reference numeral 1050 denotes a p-type semiconductor spacer layer, and 1060 denotes only one pair of layers of a p-type DBR region (a plurality of pairs are provided in an actual device). In Fig. 1, p-type semiconductor spacer layer 1050, the p-type Al _{0 .35} Ga _{0 .15} In ₀ consists of _.5 P, p-type DBR region 1060, a p-type Al _{0 .9} Ga _{0 .1} as layers and p-type Al _{0 .5} Ga _{0 .5} illustrates a band structure in a case include as layer as a pair.

For comparison purposes, the graph of FIG. 1 includes the band end 1020 of the conduction band at the point Γ, the line up 1090 of the band end of the valence band, and the pseudo Fermi levels 1092 and 1093. In addition, for simplicity, in FIG. 1, spikes, notches, etc. resulting from discontinuity of band end energy are not shown. Since the p-type layer has been examined, the band lineup of the layer doped with the p-type impurity is determined so that the Fermi level existing near the valence band is the same.

Further, in the in the Al _{0 .9} Ga _{0 .1} As constituting the p-type DBR region (1060) (p-type semiconductor multilayer film region), X point ((1010 in Fig. 1)), the band ends are at Γ points Is significantly lower than that. In particular, the band edge potential of the conduction band of the p-type Al _{0 .9} Ga _{0 .1} As adjacent to the p-type AlGaInP spacer layer is stronger by about 200 meV.

That is, a band diagram different from the band diagram (Fig. 6) disclosed in the Schneider literature can be constructed.

Based on this newly constructed band diagram, the leakage current can be examined again as follows.

Electrons are present in this p-type semiconductor spacer layer 1050 beyond the hetero gap, which is the difference between the band ends of the active layer 1070 and the p-type semiconductor spacer layer 1050. The concentration of such electrons is actually affected by the potential drop in the conduction band edge of the component, the Al _{0 .9} Ga _{0 .1} As of the adjacent p-type DBR region 1060. The undoped barrier layer 1075 in FIG. 1 is provided as necessary.

Therefore, p-type semiconductor spacer layer 1050 and a p-type Al _{0 .9} Ga _{0 .1} As almost all electrons near the interface between the 1061 is dropping toward the p-type Al _{0 .9} Ga _{0 .1} As, p It is believed that electrons having the same energy as the inside of the type semiconductor spacer layer are hardly present near the interface.

In other words, the electron concentration gradient in the p-type semiconductor spacer layer 1050 is very large, and its diffusion current component can take a very large value.

Thus, the p-type DBR region 1060 does not actually function as a barrier for carrier electrons leaking beyond the p-type semiconductor spacer layer 1050.

That is, the effective thickness of the p-type layer that contributes to suppressing leakage current beyond the p-type semiconductor spacer layer is not the total thickness of the spacer layer and the p-type DBR region, but the thickness of the p-type semiconductor spacer layer alone.

In order to examine leakage current based on this new knowledge, the leakage current was computed by following formula (1).

The leakage current density J _leak is given by the following formula 1 based on the diffusion component and the drift component of electrons leaked from the active layer to the p-type semiconductor spacer layer (D. Bour et al., Journal of Quantum Electronics, Vol. 29, No. 5 (1993) 1337):

[Equation 1]

Where q is the charge amount, D _n is the diffusion constant of the electron, m _n is the effective mass of the electron, k is the Boltzmann constant, h is Plank's constant, T is the temperature, ΔE is the hetero barrier, and L _n is the electron The diffusion length, Z is the effective electric field length, σ _p is the conductivity of the p-type spacer layer, J _total is the total injection current density, and x _p is the thickness of the p-type cladding layer.

2A shows the normalized leakage current (solid line 2091) calculated by Equation 1 above. The horizontal axis represents the thickness of the p-type semiconductor spacer layer, and the vertical axis represents the normalized leakage current. In addition, the spacer layer is assumed to be composed of AlGaInP (e.g., Al _{0 .5 0 .5} In P or _{Al 0.35 Ga 0.15 In 0.5 P)} .

The graph clearly shows that the leakage current (particularly the diffusion current component) increases rapidly in the region where the thickness of the p-type semiconductor spacer layer is about 80 nm or less. In this region, it can be assumed that the luminous efficiency is lowered, the high temperature operating characteristics are inferior, and it is difficult to obtain the entire output operation.

The thickness of the p-type semiconductor spacer layer disclosed in Crawford literature is "50 nm". The above findings show that the resulting structure is not advantageous in suppressing leakage current.

That is, the thickness of the p-type AlGaInP spacer layer typically used in red surface emitting lasers is about 50 nm, but according to the inventors' findings, in order to achieve improved high temperature operating characteristics, the thickness of this p-type spacer layer may be increased. It shows that it is necessary.

First Embodiment (Red Surface Emitting Laser Device)

Hereinafter, the red surface emitting laser element containing the multilayer film which concerns on this 1st Embodiment is demonstrated with reference to FIG.

The laser device 3000 includes a first reflector 302, a second reflector 308 including a p-type semiconductor multilayer, and an active layer 305 interposed between the first reflector 302 and the second reflector 308. ). The laser device 3000 further includes a p-type semiconductor spacer layer 307 having a thickness of 100 nm or more and 350 nm or less between the active layer 305 and the second reflecting mirror 308.

The reason why the thickness of the p-type semiconductor spacer layer is 100 nm or more and 350 nm or less is described below. However, "thickness" means the length of a lamination direction.

The dotted line 2095 in FIG. 2A is drawn to find the degree (tilt) of the change in the standardized leakage current in the region where the standardized leakage current increases significantly with respect to the thickness of the p-type semiconductor spacer layer.

This graph indicates that the thickness of the p-type semiconductor spacer layer 307 should be outside the region 2591 where the thickness is very inclined and may vary slightly depending on the composition ratio of the material constituting the spacer layer. It is shown.

On the other hand, the dotted line 2096 is drawn to find the degree (tilt) of the change in the standardized leakage current in the region where the change in the standardized leakage current is very gentle with respect to the thickness of the p-type semiconductor spacer layer 307. . The dotted line 2096 clearly shows that in the region where the thickness of the p-type spacer layer exceeds 350 nm, the change in the thickness of the spacer layer does not substantially affect the leakage current.

Referring now to FIG. 2B, the solid line 2091 shows the change in loss inside the resonator plotted against the thickness of the p-type spacer layer. In this graph, the loss caused by the reflector is not taken into account, and only the loss caused by absorption of free carriers in the p-type spacer layer and the p-type DBR layer is taken into consideration and distributed throughout the resonator length. 2B, it can be clearly seen that the loss inside the resonator increases with the thickness of the p-type spacer layer. In this regard, the thickness of the spacer layer is preferably as thin as possible. According to the above graph, even when the thickness of the p-type semiconductor spacer layer is 350 nm, the increase in the loss in the resonator is 20% or less (the loss in the resonator at 350 nm is 12.5 cm ^-1). , Assuming that the loss in the resonator at 50 nm is 10.5 cm ^-1 ).

In this manner, the thickness of the p-type semiconductor spacer layer can be 100 nm or more and 350 nm or less.

In the above description about the p-type semiconductor spacer layer, the description of the specific composition ratio is omitted.

It should be noted, however, that in Figs. 2A and 2B, the normalized leakage current is calculated based on the following portion of Equation 1 (Equation 2) while the remaining portions are assumed to be the same:

[Formula 2]

In the above calculation, the thickness of the p-type layer is assumed to be the thickness (x _p = 40 to 700 nm) of the p-type AlGaInP spacer layer. In addition, it is assumed that the doping level of the p-type impurity is 1 × 10 ¹⁸ cm ⁻³ , the electron diffusion length is 1 μm, and the total injection current density J _total is 3 kA / cm 2. In addition, in order to normalize the leakage current with respect to a spacer layer, the value of temperature T is not considered in calculation. Regarding the internal light absorption, the free carrier absorption of the entire element including the multilayer film reflector (p-type DBR region) is calculated.

The p-type semiconductor spacer layer and the p-type semiconductor multilayer film (p-type DBR region) will be described in detail below.

The band end of the conduction band at the point X of the p-type semiconductor spacer layer 307 is formed at the point X of the two layers constituting the repeating unit of the p-type DBR region (1060 in FIG. 1 and (308) in FIG. 3). The material is selected such that the conduction band end of is higher than the band edge of the high layer. In other words, the material is selected so that the conduction band end at the X point in the p-type DBR region is lower than the conduction band end of the p-type semiconductor spacer layer.

In addition, the p-type semiconductor spacer layer 307 may be formed from a layer containing aluminum, indium and phosphorus.

When the composition of the p-type semiconductor spacer layer 307 is Al _x Ga _y In _{1 -x- y} P, the ranges of x and y can be as follows.

First, in order to achieve a price matching between Al _x Ga _y In _{1 -x- y} P and GaAs, the ratio of indium ("1-xy" in the above formula) should be 0.45 to 0.55, preferably 0.48 to 0.50. .

That is, 0.45 ≦ x + y ≦ 0.55, specifically 0.50 ≦ x + y ≦ 0.52.

Typically, the barrier layer inside the active layer is composed of _{Al 0 .2 Ga 0 .3 In 0} .5 P. In order to secure a hetero barrier between the active layer and the p-type semiconductor spacer, the ratio x of aluminum may be 0.25 or more, preferably 0.30 or more, and more preferably 0.35 or more. In addition, the upper limit of the aluminum ratio in the said composition should just be 0.55 or less, Preferably it is 0.52 or less in order to achieve lattice matching.

In addition, the ratio of gallium may be zero. Thus, one example of the composition of the p-type semiconductor spacer layer is _{Al x Ga y In 1 -x- y} P ( where, x and y have the above-described relationship, i.e., 0.45≤x + y≤0.55, On the other hand, 0.25≤x≤0.55 And 0 ≦ y ≦ 0.30).

Alternatively, the composition of the p-type semiconductor spacer layer may be an _{Al x Ga y In 1 -x- y} P (0.50≤x + y≤0.52, 0.35≤x≤0.52, 0≤y≤0.17).

It should be understood, of course, that the composition may contain other impurities and the like as long as the material can be epitaxially deposited.

Further, when the proportion of indium is 0.5, i.e., the p-type Al _z Ga _{1 - z} In the case of using the _{0 .5} P spacer layer, z, for example, may be appropriately determined in the range of 0.35≤z≤0.5. When z is within this range, a spacer layer having a relatively high crystallinity can be easily formed, and the band offset between the active layer and the spacer layer can be increased.

In addition, the p-type semiconductor spacer layer 307 may use a multiple quantum barrier (MQB) structure.

In the two layers constituting the repeating unit of the second reflecting mirror 308, the composition of the layer having the high conduction band end (when both layers are composed of AlGaAs, the one with the higher aluminum ratio) has the composition of Al _x Ga _{1- x} As ( 0.70 ≦ x ≦ 1.0, preferably 0.8 ≦ x ≦ 1.0).

The p-type semiconductor multilayer film constituting the second reflector 308 is configured by stacking a plurality of repeating units each including a first layer and a second layer having different refractive indices. At least one layer of the first and second layers may contain aluminum, gallium and arsenic as described above.

In addition, of the two layers constituting the repeating unit, the composition of the layer having a low conduction band end may be Al _x Ga _1-x As (0.40 ≦ _x ≦ 0.70, preferably 0.45 ≦ _x ≦ 0.60). In this composition, this may depend on the wavelength of the light emitted from the active layer, but x is set to 0.4 or more so that the wavelength of the light emitted from the active layer is not absorbed, thereby achieving sufficient refractive index for the other layers constituting the DBR. can do. For example, when the composition of the layer is Al _x Ga _{1 - x} As, x = 0.5.

In FIG. 1, among the layers constituting the second reflecting mirror 308 (p type semiconductor multilayer film), a layer having a high conduction band end at X point is shown adjacent to the p type semiconductor spacer layer 1050. It is not necessary. For example, among the layers constituting the DBR region, a layer having a low conduction band end at X may be adjacent to the p-type semiconductor spacer layer 1050.

(a) Resonator  rescue

In order to obtain a p-type semiconductor spacer layer having the above-mentioned thickness, a resonator length larger than one wavelength is preferable. For example, a resonator length of 1.5 wavelength or more may be used.

In addition, the p-type semiconductor spacer layer (1050 of FIG. 1 and (307) of FIG. 3) may be a p-type AlGaInP spacer layer having a thickness of 100 nm or more and 350 nm or less, especially 150 nm or more and 300 nm or less.

Examples of resonator lengths include 1.5 or 2 wavelengths. To obtain this resonator length, the thickness of the p-type semiconductor spacer layer can be increased so that the resonator length is increased by 0.5 wavelength increments. Since 0.5 wavelength corresponds to about 100 nm, when combined with a conventional p-type AlGaInP layer with a thickness of about 60 nm, the thickness is 160 nm (if 0.5 wavelength is added) and 260 nm (if 1 wavelength is added). )to be. Therefore, the thickness of the p-type semiconductor spacer layer may be 150 nm or more and 300 nm or less, particularly to include the case where 0.5 wavelength is added and the case where 1 wavelength is added.

For the resonator structure of this embodiment, the resonator length may be 1.5 wavelength or more, and the upper limit of the resonator length is 4 or less wavelengths, preferably 3.5 or less wavelengths, and more preferably 2.5 or less wavelengths. "Resonator length" is the thickness in the lamination direction of the region between the first reflecting mirror and the second reflecting mirror.

Referring now to FIG. 3, the n-type semiconductor spacer layer 303 located on the substrate 301 side of the active layer 305 is not essential in terms of carrier overflow, and may be provided as necessary.

Since the leakage current of holes into the n-type semiconductor spacer layer 303 (eg, AlGaInP) is sufficiently small, the thickness of the n-type semiconductor spacer layer 303 may be about 40 nm to 80 nm.

That is, the resonator of the present invention includes an active layer 305, a p-type semiconductor spacer layer 307 and an n-type semiconductor spacer layer 303. The resonator may have an asymmetric structure in which the active layer 305 is not located at the center of the resonator length direction.

In particular, the thickness of the p-type semiconductor spacer layer 307 may be thicker than the thickness of the n-type semiconductor spacer layer 303. However, "asymmetric structure" means a configuration in which the p-type semiconductor spacer layer 307 is thicker than the n-type semiconductor spacer layer 303 and the active layer 305 is not disposed in the center of the resonator. The device configuration can be designed such that the center of the active layer aligns with the antinode (also referred to as "fold") of the light intensity standing wave inside the device.

Referring to FIG. 3, the layers 304 and 306 adjacent to the active layer 305 are each undoped spacer layers (p-type and n-type semiconductor spacer layers 307, (which may be provided as necessary). Spacer layer having a lower impurity concentration than 303). These layers 304 and 306 are not essential in this embodiment, but as barrier layers that block impurity diffusion from the p-type semiconductor spacer layer 307 and the n-type semiconductor spacer layer 303 into the active layer 305. Can be formed. The thicknesses of the layers 304 and 306 may be 10 nm or more and 50 nm or less, preferably 20 nm or more and 40 nm or less.

In an AlGaInP semiconductor laser, for example, red light emission can be obtained by using a GaInP quantum well structure for the active layer. Examples of the p-type semiconductor spacer layer 307 is _{Al 0 .35 Ga 0 .15 In 0} .5 P layer or an Al _{0 .5 0 .5} may be mentioned In P layer.

Hereinafter, the laminated constitution of the red surface emitting laser of this embodiment is given and demonstrated with a specific material.

For example, an _{Al x Ga 0 .5-x In} 0.5 P layer (0.2≤x≤0.5) of about 170 ㎚ thickness can be used as the p-type semiconductor spacer layer 307. Since the effective mass of a hole is _{Al x Ga 0 .5-x In} 0.5 P (0.2≤x≤0.5) substantially do not contribute to leakage current across the n-type semiconductor spacer layer 303 consisting of, the n-type AlGaInP The thickness of the layer can be as usual, for example about 50 nm.

The active layer 305 is designed to have a multi quantum well structure suitable for a surface emitting laser, the thickness of which is about 40 nm to about 50 nm. Therefore, it is necessary to design the resonator length of the resonator to be at least 1.5 wavelength as a whole.

Since the active layer 305 is aligned with the breaking of the internal light intensity standing wave, the active layer 305 is not located at the center of the 1.5 wavelength resonator length. Therefore, the resonator structure has an asymmetrical structure instead of the symmetrical structure common to a conventional one-wavelength resonator.

In some cases, the symmetrical structure is advantageous in that the position of the active layer can be easily aligned with the rupture of the internal light intensity standing wave, while adjusting the resonance wavelength to a desired value during crystal growth. Therefore, the thickness of the n-type AlGaInP spacer layer is increased to be equal to the thickness of the p-type AlGaInP layer. For example, the thickness of the n-type AlGaInP spacer layer can be adjusted to about 170 nm to form a resonator having a symmetrical structure. In this case, according to the above example, the resonator length is two wavelengths. Since free carrier absorption in the n-type spacer layer is less than that of the p-type layer, the problem of light absorption by thickening the n-type layer is not as serious as the p-type layer.

As a result, it is possible to provide a novel red surface emitting laser device in which the leakage current is reduced and there is no significant increase in light absorption due to the increase in the thickness of the spacer layer.

(b) other configurations

In FIG. 3, although the board | substrate 301 (for example, GaAs board | substrate) is shown, you may abbreviate | omit as needed. For example, a substrate made of GaAs and other suitable materials may be used to deposit a multilayer thereon, and then the substrate may be removed. Alternatively, the multilayer film may be transferred to another substrate, such as a silicon substrate, a silicon-on-insulator (SOI) substrate, a germanium substrate, a plastic substrate, or a transparent substrate such as a glass substrate. In order to increase heat dissipation, the light emitting element may be transferred to a silicon substrate or an SOI substrate. During transfer of the film, polishing techniques or grinding techniques may be used to remove the deposited substrate. Alternatively, it is also possible to form a sacrificial layer on the deposition substrate and then form a layer constituting the device on the sacrificial layer to facilitate the transfer of the film.

The second reflecting mirror 308 (p-type semiconductor multilayer film) may contain aluminum and arsenic. The second reflector 308 includes a plurality of units each including a first layer and a second layer having different refractive indices. At least one layer of the first layer and the second layer may be a layer containing aluminum, gallium, and arsenic.

The material of the second reflecting mirror 308 is not limited to AlAs or AlGaAs, and may be any semiconductor material having a lattice matching with the lattice of GaAs.

In addition, the first reflector 302 may be an n-type semiconductor multilayer film. An n-type AlGaInP spacer layer (303 in FIG. 3) may be provided between the first reflecting mirror 302 and the active layer 305.

The first reflector 302 need not necessarily be an n-type DBR as long as it can inject a current into the laser device 3000. If a bonding technique is available, a photonic crystal may be used as the reflector instead of the semiconductor multilayer film.

In FIG. 3, spacer layers 304 and 306 are provided between the active layer 305 and the p-type and n-type spacer layers 303, 307, but this may be omitted as necessary. In Fig. 3, the first reflecting mirror 302 (n-type DBR region) is provided on the substrate 301 side, and the second reflecting mirror 308 (p-type DBR region) is provided on the active layer, but this configuration is reversed. You may. For example, a p-type DBR region or a p-type spacer layer may be disposed between the active layer and the substrate.

An example of the configuration of the active layer 305 is a quantum well active layer including a GaInP layer and an AlGaInP layer. In this embodiment, the said structure may be any structure as long as it can output red light (wavelength 0.6-0.73 micrometer, especially 0.63 micrometer-0.72 micrometer light). For example, an active layer having a double heterostructure or a quantum dot structure may be used, or other suitable material such as AlGaInPN may be used as the active layer. Alternatively, a plurality of active layers may be used, as described below with reference to FIGS. 8 to 10. For example, as shown in FIG. 8, two or more active layers can be used.

As described above, the resonator includes an active layer 305, a p-type semiconductor spacer layer 307, and an n-type semiconductor spacer layer 303, and has an asymmetric structure in which the active layer is not disposed at the center of the resonator length direction. You can also take

Here, the thickness of the p-type AlGaInP semiconductor spacer layer 307 may be thicker than the thickness of the n-type AlGaInP semiconductor spacer layer 303.

Further, in the present embodiment, the thickness of the layer in the DBR region can be designed to constitute a vertical resonator type surface emitting laser, but the emission does not need to be strictly vertical as long as surface emitting is possible.

This embodiment is suitable for the laser element required to achieve laser operation at high temperature. In particular, the present embodiment is effective when applied to a single transverse mode laser device exhibiting high luminescence intensity.

Second embodiment

Hereinafter, the red surface emitting laser element containing the multilayer film which concerns on 2nd Embodiment of this invention is demonstrated with reference to FIG. 3 similarly to 1st Embodiment.

The device includes a first reflector 302, a second reflector 308 including a p-type AlGaAs semiconductor multilayer, and an active layer 305 interposed between the first reflector and the second reflector. The device also includes a p-type AlInP or AlGaInP semiconductor spacer layer 307 having a thickness of 100 nm or more and 350 nm or less between the active layer 305 and the second reflecting mirror 308.

Further, the p-type semiconductor spacer layer may contain both AlInP and AlGaInP provided that the thickness of the p-type semiconductor spacer layer is entirely within the above range.

According to this structure, the novel red surface emitting laser element in which leakage current is reduced is provided.

However, the expressions "AlGaAs" and "AlGaInP" mean that the former layer contains aluminum, gallium and arsenic, and the latter layer contains aluminum, gallium and phosphorus. The composition ratio is not particularly limited as long as it can epitaxially grow each layer and realize red light emission. It goes without saying that the matters described in the first embodiment described above can be applied to the laser device in the second embodiment as long as there is no contradiction.

Third embodiment

Hereinafter, the red surface emitting laser element including the multilayer film according to the third embodiment will be described with reference to FIG. 3 as in the above-described embodiment.

The device includes a first reflector 302, a second reflector 308 including a p-type semiconductor multilayer, an active layer 305 interposed between the first reflector 302 and the second reflector 308, and the active layer. And a p-type semiconductor spacer layer 307 interposed between the second reflecting mirror and the second reflecting mirror.

As already described with reference to FIG. 1, the conduction band end at the point X of the p-type semiconductor multilayer film is lower than that of the p-type semiconductor spacer layer 307, and the stacking direction of the p-type semiconductor spacer layer 307 is lower. The thickness is 100 nm or more and 350 nm or less.

Although the leakage current cannot be sufficiently reduced due to the presence of the second reflector 308 including the p-type semiconductor multilayer film, the leakage current is reduced by adjusting the thickness of the p-type semiconductor spacer layer 307 to 100 nm or more and 350 nm or less. It becomes possible (refer FIG. 2A).

As a matter of course, the laser device of the third embodiment can be applied as long as there is no contradiction.

Fourth Embodiment ( Image Forming Device  And image display device)

The red surface emitting laser element described in the first to third embodiments can be applied to, for example, an image forming apparatus or an image display apparatus.

When the element is applied to the image forming apparatus, as shown in FIGS. 9A and 9B, the image forming apparatus reflects the red surface emitting laser element 914 and the laser light output from the laser element to perform scanning. And an optical deflector 910. The optical deflector 910 can have any structure as long as it can reflect a laser beam and scan a reflection direction.

Examples of the optical deflector 910 include a reflector formed by rocking a laminate made of silicon or the like using a multifaceted mirror, a polygon mirror, and a micro electro mechanical system (MEMS) technique.

When the apparatus is an electrophotographic apparatus, a drum-shaped photosensitive member 900, a charger 902, a developing unit 904, and a fixing unit 908 for forming an electrostatic latent image by a beam deflected by the optical deflector 910. ) Is installed. Details of this electrophotographic apparatus will be described with reference to the following examples.

The red surface emitting laser element may be used in combination with the deflector and other related components to form an image display apparatus such as a display.

Alternatively, it is also possible to arrange many red surface emitting laser elements in an array to form a multi-beam image forming apparatus.

Example  One

Hereinafter, Example 1 will be described. 3 is a schematic cross-sectional view of the layer structure of the red surface emitting laser device of Example 1. FIG.

VCSEL according to the first embodiment is an n-type GaAs substrate (301), n-type _{Al 0 .9 Ga 0 .1 As /} Al 0 .5 Ga 0 .5 As multilayer reflecting mirror (302), n-type Al _{0 .35} Ga _{0 .15} In _{0 .5} P spacer layer 303, undoped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer _{(304), Ga 0 .56 In} 0 .44 P / Al 0 .25 Ga _{0 .25} In _{0 .5} P quantum well active layer 305, a non-doped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer (306), p-type Al _{0 .5 0 .5} In P spacer layer 307, a p-type _{Al 0 .9 Ga 0 .1 As /} Al 0 .5 Ga 0 .5 As multilayer reflector 308 and the p-type GaAs contact layer 309. As a result, a red surface emitting laser for emitting light having a wavelength of 680 nm is formed.

First, n-type _{Al 0 .9 Ga 0 .1 As /} Al 0 .5 Ga 0 .5 describes As multilayer reflector 302 and the p-type _{Al 0.9 Ga 0.1 As / Al 0.5} Ga 0.5 As multilayer reflector 308 do. Al _{0 .9} Ga _{0 .1} As layer and Al _0.5 Ga _0.5 As layer is formed to have an optical thickness of one-quarter wavelength, respectively.

In an actual element, in order to reduce the electrical resistance, Al _{0 0 .1 .9} Ga As layer and Al _0.5 Ga _0.5 As gradient composition layer having a thickness of about 20 ㎚ between layers it is provided.

In this case, the total thickness including the thickness of the composition gradient layer is designed to be an optical thickness of 1/4 wavelength. In order to allow current to flow, the p-type multilayer film reflector 308 is doped with impurities such as carbon or zinc, which act as acceptors. In addition, the n-type multilayer film reflector 302 is doped with impurities, such as silicon or selenium, which act as donors. In order to reduce light absorption in the multilayer film reflector as much as possible, modulation doping may be performed such that the doping amount is low at the break of the light intensity standing wave in the multilayer film reflector, and the doping amount is high at the node (ie, the node). Do.

In this embodiment, light is output from the epitaxial layer surface, that is, from the p-type layer side. In this manner, the p-type multilayer film reflector 308 includes about 36 pairs of repetitive pairs to form a reflector exhibiting optimum light output efficiency. Since no light is output from the n-type layer side, the n-type multilayer film reflector 302 is designed to include about 60 pairs of repetitive pairs to increase the reflectance as much as possible and to lower the threshold current.

In the p-type multilayer film reflector 308 is the one to three pairs of position about 30 ㎚ can be inserted into the thickness of the Al _{0 .98} Ga _{0 .02} As layer, the Al _{0 .98} Ga _{0 .02} As layer from the active layer It can also be selectively oxidized to form a current-confining structure.

Hereinafter, a method of manufacturing the resonator will be described.

a p-type Al _{0 .5 0 .5} In P, so we set the thickness of the spacer layer 307 in a range from 100 ㎚ 350 ㎚, the cavity length is 1.5 wavelength as shown in Figure 4 instead of 1 wavelength usually used.

Since the emission wavelength is 680 nm, the 1.5 wavelength gives an optical thickness of 1020 nm. The layers constituting the resonator are all composed of AlGaInP, but AlGaInP materials having different composition ratios are used for the active layer, the barrier layer, the spacer layer, and the other layers. Therefore, the thickness of each layer needs to be determined based on the refractive index so that the resonator length is 1.5 wavelength.

In order to maximize the interaction between the light and the carrier, it is necessary to arrange the active layer on the standing wave 403. That is, the active layer 305 is disposed at a position 1/3 of one end of 1020 nm, the n-type layer is disposed in a shorter region (left side of the active layer 305 in FIG. 4), and the p-type layer is longer. It is arrange | positioned at the side (right side of the active layer 305 in FIG. 4).

Considering the above conditions, a practical example will be described in detail as follows.

The active layer 305 includes four 6 ㎚ GaInP quantum wells and three _{6 ㎚ Al 0 .25 Ga 0 .25} In 0 .5 P barrier layer. In addition, the actual thickness of the active layer 305 is 42 nm.

Since the refractive indices of the GaInP layer and the _{Al 0 .25 Ga 0 .25 In 0} .5 P layer at the emission wavelength 680 ㎚ were 3.56 and 3.37, and the optical thickness of the active layer 146 ㎚.

Half of the optical thickness of the active layer region (73 ㎚), undoped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer (304) Al _{0 .35,} and the optical thickness of n-type Ga _{0 .15} In ₀ The sum of the optical thicknesses of the _.5 P spacer layers 303 needs to be 340 nm, which is 1/3 of 1020 nm.

Thus, the non-doped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer 304 is formed to have a thickness of 20 ㎚, n-type _{Al 0 .35 Ga 0 .15 In 0} .5 P spacer layer 303 is formed to have a thickness of 60.5 nm. Since the refractive indices of the layers 304 and 303 are 3.37 and 3.30, respectively, the optical thickness of these two layers is 267 nm.

That is, the sum of 73 nm and 267 nm, which are half of the optical thickness of the active layer 305, is 340 nm, and as shown in FIG. 4, the center of the active layer 305 is aligned with the standing wave 403.

For p-type layer side, one half of the optical thickness of the active layer (305) (73 ㎚) and undoped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306 and a p-type Al _{0 .5 0 .5} In P spacer layer ( It is necessary to make the optical thickness of 307 remain the remainder, that is, 680 nm.

an n-type layer side, but using _{Al 0 .35 Ga 0 .15 In 0} .5 P layer, p-type layer side is used, and the Al _{0 .5 0 .5} In P layer in order to increase the potential barrier for interrogating a hedge Doping to about 1 × 10 ¹⁸ cm ^-3 . Zinc or magnesium can be used as the dopant.

Barrier layer 306 is formed to have a thickness of 20 ㎚, p-type Al _{0 .5 0 .5} In P spacer layer 307 is formed to have a thickness of 167.6 ㎚. Since the refractive indices of these layers 306 and 307 are 3.37 and 3.22, respectively, the sum of the optical thicknesses of these two layers is 607 nm. Moreover, the sum of this 697 nm and 73 nm which is half of the optical thickness of the active layer 305 is 680 nm.

As described above, the optical thicknesses of the n-type layer including the undoped barrier layer, the active layer and the p-type layer including the undoped barrier layer are 267 nm, 146 nm and 607 nm (1020 nm in total), respectively. This sum corresponds to the optical thickness in the case of a 1.5 wavelength resonator.

Moreover, the thickness of a p-type layer is 167.6 nm, and this is in the range of 100 nm or more and 350 nm or less.

Multilayer film reflectors are formed on both sides of this resonator. The n side and the p side of the multilayer film reflector are arranged so that the interface between the resonator and the multilayer film reflector is aligned with the breaking of the standing wave.

Specifically, the low refractive index material, i.e., Al _{0 .9} Ga _{0 .1} As layer 402 is in contact with the resonator, wherein the Al _{0 .9} Ga _{0 .1} and adjacent As layer 402 refractive index material, i.e., , Al Ga _{0 .5 0 .5} As the layer 401 is disposed. The necessary number of pairs of these layers 401, 402 is formed repeatedly (36 pairs on the p side, 60 pairs on the n side).

In actual device fabrication, a wafer having a layer of the above thickness is first formed by a crystal growth technique.

For example, the layers are formed by an organometallic compound vapor deposition apparatus or a molecular beam epitaxy apparatus. After the wafer is formed, the laser device 5000 shown in Fig. 5 is formed by a normal semiconductor process. However, in FIG. 5, the layer which has the same function as the layer demonstrated with reference to FIG. 3 is represented with the same number.

The post is formed by photolithography and semiconductor etching, and the current confining layer 502 is formed by selective oxidation. Thereafter, the insulating film 503 is formed, partially removed to expose a portion of the p-type GaAs contact layer 309 for contact, and the p-side electrode 504 is formed. Finally, the n-side electrode 501 is formed on the back side of the wafer to finish manufacturing the device.

The device fabricated as described above can achieve high temperature operation and overall output operation, thereby expanding the application range of the red surface emitting laser device.

The above description provides a method of manufacturing one device.

When fabricating a plurality of elements integrated in an array shape, for example, when arranging 32 elements in a 4 占 8 array shape at 50 占 퐉 pitch, a photomask having a target element arrangement is used from an initial stage. Subsequently, using the above epiwafer, a plurality of elements arranged in an array shape can be formed simultaneously by the same element formation process. That is, a red surface emitting laser array can be obtained easily by using the mask which has a target pattern.

However, the device is formed using an n-type GaAs substrate, and a p-type layer is disposed thereon. Alternatively, a p-type GaAs substrate may be used for device formation, and the device may include an n-type layer thereon.

Example  2

The second embodiment will be described below. 7 is a schematic cross-sectional view of the layer structure of the red surface emitting laser element 7000 of the second embodiment.

VCSEL structure of this embodiment is an n-type GaAs substrate (301), an n-type AlAs / Al Ga _{0 .5 0 .5} As multilayer reflecting mirror (701), _.15 n-type _{Al 0 .35 Ga 0 In 0 .5} P spacer layer 303, undoped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer 304, a _{1 Ga 0 .56 In 0 .44 P} / Al 0 .25 Ga 0 .25 In 0 .5 P quantum well active layer _{(702), Al 0 .25 Ga} 0 .25 In 0 .5 P intermediate barrier layer 703, a _{2 Ga 0 .56 In 0 .44 P} / Al 0 .25 Ga 0 .25 In 0 _.5 p quantum well active layer 704, undoped _{Al 0 .25 Ga 0 .25 In 0} .5 p barrier layer (306), p-type _{Al 0 .35 Ga 0 .15 In 0} .5 p spacer layer ( 705), a p-type _{Al 0 .9 Ga 0 .1 As /} Al 0 .5 Ga 0 .5 As multilayer reflector 308 and the p-type GaAs contact layer 309. As a result, a red surface emitting laser for emitting light having a wavelength of 680 nm is formed.

an n-type multilayer film reflector 701 is composed of AlAs instead of Al _{0 .9} Ga _{0 .1} As. The reason is that AlAs has a low thermal resistance, which can reduce the thermal resistance of the device as a whole.

a p-type _{Al 0 .9 Ga 0 .1 As /} Al 0 .5 Ga 0 .5 As multilayer film reflector 308 is the same as that of Example 1 (Fig. 3).

As shown in Fig. 7, in this embodiment, a periodic gain structure including two multiple quantum well structures is used. According to this structure, a high light emission output can be easily obtained by increasing the light restraint ratio and the mode gain.

In addition to using the periodic gain structure, the resonator length is set to 2.5 wavelengths as shown in Fig. 8 so that the thickness of the p-type AlGaInP layer is 100 nm or more and 350 nm or less.

Hereinafter, the layer structure of the resonator will be described with reference to FIG. 8.

Since the resonant wavelength is 680 nm and the resonator length is 2.5 wavelength, the optical thickness thereof is 1700 nm.

The layers in the resonator are all composed of AlGaInP. However, since AlGaInP materials with different composition ratios are used for the active layer, barrier layer, spacer layer and other layers, it is necessary to determine the thickness of each layer based on its refractive index so that the resonator length is 2.5 wavelength.

In order to maximize the interaction between the light and the carrier, the active layers 702 and 704 need to be disposed in the rupture 403 of the internal light intensity standing wave. That is, the active layer is disposed at positions 1/5 and 2/5 at 1700 nm from one end of 1700 nm, respectively, and an n-type layer is disposed at the short region (left side in FIG. 8) and the long region (FIG. 8). On the right side).

Considering the above conditions, a practical example will be described in detail as follows.

The first active layer 702 and the second active layer 704 includes four 6 ㎚ including GaInP quantum wells and three _{6 ㎚ Al 0 .25 Ga 0 .25} In 0 .5 P barrier layer, and the physical thickness of each of 42 nm. Since the refractive indices of the GaInP layer and at 680 ㎚ _{Al 0 .25 Ga 0 .25 In 0} .5 P layer are respectively 3.56 and 3.37, the optical thickness of each active layer is 146 ㎚.

The optical thickness of a half (73 ㎚) and undoped Al Ga _{0 .25 0 .25} regions of the active layer In _{0 .5} P barrier layer 304 and the n-type _{Al 0 .35 Ga 0 .15 In 0} .5 P The sum of the optical thicknesses of the layers 303 needs to be 340 nm.

Thus, the undoped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer 304 is formed to have a thickness of 20 ㎚, n-type _{Al 0 .35 Ga 0 .15 In 0} .5 P layer ( 303) is formed to have a thickness of 60.5 nm. Since the refractive indices of each of the layers 304 and 303 are 3.37 and 3.30, respectively, the sum of the optical thicknesses of these two layers is 267 nm. The sum of this 267 nm and 73 nm which is half of the optical thickness of the first active layer 702 is 340 nm.

That is, as shown in FIG. 8, the center of the first active layer 702 is aligned with the wave 403 of the standing wave. Next, half of the optical thickness of the first active layer 702 (73 nm) and half of the optical thickness of the Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703 and the optical thickness of the second active layer 704 (73 nm). The sum of must be 340 nm.

Since the refractive index of the _{Al 0 .25 Ga 0 .25 In 0} .5 P intermediate barrier layer 703 is 3.37, when the thickness is 57.6 ㎚, the _{Al 0 .25 Ga 0 .25 In 0} .5 P intermediate barrier layer The optical thickness of 703 needs to be 194 nm. The total of these 194 nm, 73 nm and 73 nm is 340 nm. Therefore, the center of the second active layer 704 is aligned with another 403 of standing waves as shown in FIG.

Alternatively, the _{Al 0 .25 Ga 0 .25 In 0} .5 P doped with magnesium or zinc to the portion of the middle barrier layer 703 made of a layer of a p-type layer, by the first active layer 702 It is also possible to increase the hole injection efficiency.

p side, one half of the optical thickness of the active layer (704) (73 ㎚) and a non-doped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306 and a p-type Al _{0 .5 0 .5} In the P layer 705 The sum of the optical thicknesses needs to be the remainder, that is, 1020 nm.

Barrier layer 306 is formed to have a thickness of 20 ㎚, p-type Al _{0 .5 0 .5} In P layer 705 is formed to have a thickness of 273.2 ㎚. Since the refractive indices of these layers 306 and 705 are 3.37 and 3.22, respectively, the sum of the optical thicknesses of these two layers is 947 nm. The sum of this 947 nm and half of the optical thickness of the second active layer 704 is 1020 nm. The optical thickness of the n-type layer including the undoped barrier layer, the sum of the optical thicknesses of the two active layers including the intermediate barrier layer, and the p-type layer including the undoped barrier layer were 267 nm, 486 nm and 947 nm, respectively. Therefore, the sum is 1700 nm, which corresponds to the optical thickness of the 2.5 wavelength resonator. In addition, the thickness of the p-type AlGaInP layer is formed to be 273.2 nm, and the allowable range thereof may be 100 nm or more and 300 nm or less.

Multilayer film reflectors are formed on both sides of this resonator. The n-side and p-side multilayer reflectors are arranged so that the interface between the resonator and the multilayer reflector is aligned with the standing wave breakage.

Specifically, Al _{0 0 .1 .9} Ga As layer 402 of the layers made of a low refractive index material, i.e., n-side of the AlAs layer 801 and the p-side is in contact with the resonator. In addition, the arrangement of these layers 801, adjacent to the (402) on the n-side and p-type Al _{0 .5 0 .5} Ga As layer 401. The number of pairs required on each side (36 pairs on the p side and 60 pairs on the n side) is repeated.

Next, as described in Example 1, a device may be manufactured or an array of devices may be manufactured.

Example  3

Hereinafter, the red surface emitting laser element applied to the red surface emitting laser array is demonstrated. 9A and 9B show the configuration of the electrophotographic image forming apparatus including the red surface emitting laser array of this embodiment. 9A is a top view of the image forming apparatus, and FIG. 9B is a side view of the apparatus.

The image forming apparatus shown in Fig. 9 includes a photosensitive member 900, a charger 902, a developing device 904, a transfer charger 906, a fixing unit 908, a rotating face mirror 910, a motor 912, and a red surface. A light emitting laser array 914, a reflector 916, a collimator lens 920, and an f-θ lens 922.

9A and 9B, the motor 912 rotates the rotating polygon mirror 910. The rotating polygon mirror 910 of this embodiment has six reflective surfaces.

The red surface emitting laser array 914 is a recording light source. This red surface emitting laser array 914 flashes in accordance with an image signal by a laser driver (not shown). The modulated laser light is applied to the rotating multifaceted mirror 910 from the red surface emitting laser array 914 through the collimator lens 920.

The rotating polygon mirror 910 rotates in the direction of the arrow. The laser light output from the red surface emitting laser array 914 is reflected by the rotating mirror mirror 910 to form a deflection beam that continuously changes the deflection angle with the rotation of the rotating polygon mirror 910. The reflected light is reflected by the reflector 916 by correcting distortion aberration or the like by the f-θ lens 922, and scans the photoconductor 900 in the main scanning direction while irradiating the photoconductor 900. At this time, an image corresponding to a plurality of lines corresponding to the red surface emitting laser array 914 is formed in the main scanning direction by the reflection of the beam deflected by one surface of the rotating polygon mirror 910. In this embodiment, an image corresponding to four lines is formed simultaneously using a 4 x 8 red surface emitting laser array.

The photosensitive member 900 is previously charged by the charger 902. The photosensitive member 900 is sequentially exposed by scanning of laser light to form an electrostatic latent image. In addition, the photosensitive member 900 is rotated in the direction of the arrow. The formed electrostatic latent image is developed by the developing device 904, and the obtained visible image is transferred to the transfer paper (not shown) by the transfer charger 906. After the transfer paper onto which the visible image is transferred is conveyed to the fixing unit 908 and the image is fixed, it is discharged out of the apparatus.

In this embodiment, a 4x8 red surface emitting laser array is used, but other types of arrays can be used. For example, an m × n red surface emitting laser array (m, n: natural number) may be used.

As described above, by using the red surface emitting laser array in the electrophotographic image forming apparatus, it is possible to obtain an image forming apparatus that realizes high speed and high precision printing.

In some cases, such as when the device is applied to a light source of an electrophotographic feast, laser operation is required up to 60 ° C. while achieving a single yellow direction mode. In general, in order to achieve a single transverse mode, it is necessary to narrow the light emitting area (4 μm or less in diameter). Even when the injection current amount is the same, the actual current density increases and the leakage current also increases.

According to the present invention, a novel red surface emitting laser device having improved temperature characteristics is provided.

11 shows an example of a laser display incorporating the laser element 1201 of the present embodiment. In FIG. 11, the laser display comprises a first deflection means 1202 and a second deflection means 1211. The scan trajectory on the second deflection means 1211 formed by the first deflection means 1202 is indicated by reference numeral 1210. Reference numeral 1212 denotes light deflected by the second deflection means 1211, 1213 denotes a specific plane, 1214 denotes a range within the plane 1213 scanned by the deflected light, ( 1215 schematically shows the trajectory of the scan line on the plane 1213. Reference numeral 1203 also denotes the light direction of the laser element 1201. Reference numerals 1205 and 1206 denote the deflected light directions, respectively.

The first deflection means 1202 and the second deflection means 1210 deflect light in the horizontal direction and the vertical direction, respectively. As a result, the area scanned by the deflected light becomes two-dimensional.

Example  4

The fourth embodiment will be described below. In the fourth embodiment, a periodic gain structure including two multiple quantum well structures is used. According to this configuration, the light confinement ratio and the mode gain can be increased, and high light emission output can be easily obtained.

In addition to the periodic gain structure, a two-wavelength resonator is used as shown in FIG. 10 to adjust the thickness of the p-type AlGaInP layer to 100 nm or more and 350 nm or less.

Hereinafter, the layer structure of the resonator will be described with reference to FIG. 10.

Since the resonant wavelength is 680 nm and the resonator length is two wavelengths, the optical thickness thereof is 1360 nm. The layers in the resonator are all composed of AlGaInP, but AlGaInP materials with different composition ratios for the active layer, barrier layer and spacer layer are used. Therefore, the thickness of each layer needs to be determined according to its refractive index so that the resonator length is two wavelengths. Further, in order to maximize the interaction between the light and the carrier, it is necessary to align the active layers 702 and 704 with the rupture 403 of the internal light intensity standing wave. In particular, the active layer is disposed at a position of 1/4 and a position of 1/2 at 1360 nm, respectively, from the end portion of 1360 nm, and an n-type layer is disposed at the short region (left side in FIG. 10) and the long region (FIG. 10). On the right side).

Considering the above conditions, a practical example will be described in detail as follows.

The first active layer 702 and the second active layer 704 includes four 6 ㎚ including GaInP quantum wells and three _{6 ㎚ Al 0 .25 Ga 0 .25} In 0 .5 P barrier layer, and the physical thickness of each of 42 nm.

Since the refractive indices of the GaInP layer and the _{Al 0 .25 Ga 0 .25 In 0} .5 P layer at a wavelength of 680 ㎚ were 3.56 and 3.37, these optical thickness of each active layer is 146 ㎚. The half of the optical thickness of the active region (73 ㎚) and a non-doped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer 304 and the n-type Al _0.35 Ga _0.15 In _0.5 P layer of the (303) The sum of the optical thicknesses needs to be 340 nm.

Undoped _{Al 0 .25 Ga 0 .25 In 0} .5 P barrier layer 304 is formed to have a thickness of 20 ㎚, n-type _{Al 0 .35 Ga 0 .15 In 0} .5 P layer 303 Is formed to have a thickness of 60.5 nm. Since the refractive indices of these layers 304 and 303 are 3.37 and 3.30, respectively, the sum of the optical thicknesses of these two layers is 267 nm. The sum of 267 nm and half (73 nm) of the optical thickness of the first active layer 702 is 340 nm. That is, as shown in FIG. 10, the center of the first active layer 702 is aligned with the wave 403 of the standing wave. Next, the optical thickness, a second active layer 704 of the half of the optical thickness of the first active layer (702) (73 ㎚) _{and, Al 0 .25 Ga 0 .25 In} 0 .5 P intermediate barrier layer 703 The sum of half the optical thickness of (73 nm) needs to be 340 nm. Since the refractive index of the Al _0.25 Ga _0.25 In _0.5 P intermediate barrier layer 703 is 3.37, when the thickness of the layer 703 is 57.6 nm, the optical thickness of the intermediate barrier layer 703 needs to be 194 nm. . Therefore, their sum will be 340 nm. Therefore, the center of the second active layer 704 is also aligned with the standing wave 403 as shown in FIG. 10. Alternatively, a portion of the AlGaInP intermediate barrier layer 703 may be doped with magnesium or zinc to make the layer p-type, thereby increasing the injection efficiency of holes into the first active layer 702.

p side, of the optical thickness of the second active layer 704, half (73 ㎚) and a non-doped Al _0.25 Ga _0.25 In _0.5 P barrier layer 306 and a p-type Al _{0 .5 0 .5} In P layer (705 The total of the optical thicknesses of?) Needs to be the remaining 680 nm. When the thickness of the barrier layer 306 is 20 nm and the thickness of the p-type Al _0.5 In _0.5 P layer 705 is 167.6 nm, the refractive indices of these layers 306 and 705 are 3.37 and 3.22, respectively, The sum of the optical thicknesses of the two layers is 607 nm. The sum of this 607 nm and 73 nm which is half of the optical thickness of the second active layer 704 is 680 nm. The optical thickness of the n layer including the undoped barrier layer, the sum of the optical thicknesses of the two active layers including the intermediate barrier layer, and the optical thickness of the p-type layer including the undoped barrier layer are 267 nm and 486 nm, respectively. And 607 nm, their sum is 1360 nm, which corresponds to the optical thickness of the two-wavelength resonator. The thickness of the p-type AlGaInP layer is 167.6 nm, which is in the range of 100 nm or more and 300 nm or less. Multilayer film reflectors are formed on both sides of this resonator. The n-side and p-side multilayer film reflectors are arranged so that the interface between the resonator and the multilayer film reflector is aligned with the standing wave. Specifically, Al _{0 0 .1 .9} Ga As layer 402 of the layers consisting of a low-refractive-index material, i.e., n-side of the AlAs layer 801 and the p-side is in contact with the resonator. These layers 801, 402, the Al _{0 .5} Ga _{0 .5} As layer 401 is disposed on the n-side and p-side. Then, the necessary numbers (about 36 pairs on the p side and about 60 pairs on the n side) are repeated for each side.

Example  5

Fig. 12 is a graph showing the relationship (solid line) between the maximum output and the environmental temperature of the red surface emitting laser having the multilayer structure explained in this embodiment. The red surface emitting laser has the configuration shown in FIG. 10 described with reference to FIG. 10. p-type semiconductor spacer layer 705 is a p-type Al _{0 .5 0 .5} In P layer (thickness: 167.6 ㎚) a. However, layer 801 in FIG 10 is composed of Al _{0 .9} Ga _{0 .1} As instead of AlAs. 12, the dotted line, while the p-type semiconductor spacer layer Al _{0 .35} Ga _{0 .15} In _{0 .5} P is composed of those having a thickness of 60.5 ㎚, the remaining configuration is the same layer as that of the device indicated by the solid line in the graph The characteristics of the device are shown.

As described above, the leakage current amount tends to increase with the environmental temperature, and the light output tends to decrease with the increase of the environmental temperature. While light emission from the device of the prior art (dashed line in FIG. 12) stopped at an environmental temperature of 75.2 ° C, the laser device of this embodiment achieves light emission up to 84.1 ° C. When comparing the maximum outputs of the two devices at 60 ° C., the maximum output of the device of this embodiment is about 40% larger than the conventional one. That is, according to the device of the present embodiment, it is possible to realize a red surface emitting laser capable of operating at high temperature by reducing leakage current.

In this case, however, an AlAs layer having a low thermal resistance is used as the low refractive index layer constituting the lower DBR disposed on the substrate side. In this case, the heat generated inside the laser device can be easily escaped, so that the temperature rise inside the device can be suppressed.

Table 1 below shows examples of p-type spacer layers having various thicknesses. In the table, _{0 .5} Al as a p-type spacer layer In _{0 .5} P layer is used and, the _{Al 0 .35 Ga 0 .15 In 0} .5 P layer as the n-type spacer layer is used, p-side and n each side has an undoped barrier layer is _{Al 0 .25 Ga 0 .25 in 0} .5 P layer is used in. Quadrupole Ga _{0 .5} In _{0 .5} when the _{P / Al 0 .25 Ga 0 .25} In 0 .5 P Quantum Well utilized as an active layer, that has a thickness of 42 ㎚. When a periodic gain structure is used, the thickness including the intermediate undoped barrier layer is 141.6 nm for the double periodic gain structure and the thickness including the two intermediate undoped barrier layers for the triple period gain structure. 241.2 nm.

In Examples 1, 2 and 4, the thickness of the p-type spacer layer is 167.6 nm or 273.2 nm. However, as shown in Table 1, the thickness of the p-type spacer layer is adjusted to a desired value (100 nm or more and 350 nm or less) by appropriately adjusting the resonator length and the thickness of the active layer, the undoped barrier layer, and the n-type spacer layer. Can be adjusted.

If the resonator length is required to be an integral multiple of the designed wavelength and the center of the active layer is required to align with the break of the standing wave, the thickness of the p-type spacer does not take a continuous value. As shown in Table 1, by adjusting the thickness of the undoped barrier layer, it becomes possible to adjust to some extent within the range defined in the present invention.

Active layer thickness (nm) p-type spacer layer thickness (nm) p-side undoped barrier layer thickness (nm) n-type spacer layer thickness (nm) n-side undoped barrier layer thickness (nm) Resonator length (wavelength) Reference One 42.0 100.0 84.6 60.5 20 1.5 2 42.0 150.0 36.8 43.3 36.8 1.5 3 42.0 167.6 20 60.5 20 1.5 4 4 42.0 273.2 20 60.5 20 2 5 141.6 167.6 20 60.5 20 2 10 6 42.0 300.0 95.2 60.5 20 2.5 7 42.0 350.0 47.5 32.4 47.5 2.5 8 141.6 273.2 20 60.5 20 2.5 8 9 42.0 237.2 20 163.5 20 2.5 10 42.0 350.0 47.5 135.4 47.5 3 11 141.6 350.0 47.5 60.5 20 3 12 141.6 252.2 40 143.1 40 3 13 141.6 252.2 40 246.1 40 3.5 14 141.6 350.0 47.5 135.4 47.5 3.5 15 141.6 350.0 47.5 238.4 47.5 4 16 241.2 252.2 40 246.1 40 4

As mentioned above, although this invention was demonstrated with reference to the Example, it should be understood that this invention is not limited to these disclosed Example. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent configurations and functions.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a lineup of band ends of an active layer, a p-type semiconductor spacer layer and a p-type semiconductor multilayer film region of a red surface emitting laser;

FIG. 2A shows the relationship between the p-type semiconductor spacer layer thickness and the normalized leakage current, and FIG. 2B shows the relationship between the p-type semiconductor spacer layer thickness and the optical loss inside the resonator;

3 is a schematic cross-sectional view showing the layer structure of a red surface emitting laser according to the first embodiment;

4 is a schematic cross-sectional view showing the structure of a resonator of Example 1;

5 is a schematic cross-sectional view of the laser device of Example 1;

6 is a band diagram cited from Schneider literature;

7 is a schematic cross-sectional view showing the layer structure of a red surface emitting laser of Example 2;

8 is a schematic sectional view showing a resonator structure of Example 2;

9A and 9B are schematic views of an image forming apparatus;

10 is a schematic sectional view showing a resonator structure of a fourth embodiment;

11 is a schematic diagram of an image display device;

12 is a graph showing the temperature characteristic of the device of Example 5. FIG.

<Explanation of symbols for the main parts of the drawings>

301: substrate 302: first reflector

305: active layer 307: p-type semiconductor spacer layer

308: second reflector 401: Al _{0 .5 0 .5} Ga As layer

_{402: Al 0 .9 Ga 0 .1} As layer

403: The recovery of the internal light intensity standing wave

501: n-side electrode 502: n-current constrained layer

503: insulating film 504: p-side electrode

701: n-type AlAs / Al Ga _{0 .5 0 .5} As multilayer film reflector

702: No. _{1 Ga 0 .56 In 0 .44 P} / Al 0 .25 Ga 0 .25 In 0 .5 P quantum well active layer

_{703: Al 0 .25 Ga 0 .25} In 0 .5 P intermediate barrier layer

704: No. _{2 Ga 0 .56 In 0 .44 P} / Al 0 .25 Ga 0 .25 In 0 .5 P quantum well active layer

705: p-type Al _{0 .5 0 .5} In P spacer layer 801: AlAs layer

900: photosensitive member 902: electrical charging

904: developer 906: warrior warrior

908: fixing machine 910: rotating multi-faceted mirror (optical deflector)

912: motor 914: 면 red surface emitting laser array

916: reflector 920: collimator lens

922: f-θ lens

Claims (20)

First reflecting mirror; a second reflector including a p-type semiconductor multilayer film; An active layer between the first reflecting mirror and the second reflecting mirror; And And a p-type semiconductor spacer layer between said active layer and said second reflector and having a thickness of 100 nm or more and 350 nm or less. The red surface emitting laser device according to claim 1, wherein the p-type semiconductor spacer layer has a thickness of 150 nm or more and 300 nm or less. The red surface emitting laser device of claim 1, wherein the p-type semiconductor spacer layer contains aluminum, indium, and phosphorus. The method of claim 1, wherein the p-type semiconductor spacer layer containing an _{Al x Ga y In 1 -x- y} P ( where, 0.45≤x + y≤0.55, 0.25≤x≤0.55 and 0≤y≤0.30) Red surface-emitting laser element, characterized in that. The method of claim 4, wherein the p-type semiconductor spacer layer containing an _{Al x Ga y In 1 -x- y} P ( where, 0.50≤x + y≤0.52, 0.35≤x≤0.52 and 0≤y≤0.17) Red surface-emitting laser element, characterized in that. The red surface emitting laser device according to claim 1, wherein the p-type semiconductor multilayer film contains aluminum and arsenic. The semiconductor device of claim 1, wherein the p-type semiconductor multilayer film includes a plurality of pairs of stacked layers, each pair including a first layer and a second layer having different refractive indices; And at least one of the first and second layers contains aluminum, gallium and arsenic. The red surface emitting laser device according to claim 1, wherein the second reflecting mirror is made of a semiconductor material having a lattice matching with GaAs. The red surface emitting laser device of claim 1, wherein the active layer is a quantum well active layer including a layer made of GaInP and a layer made of AlGaInP. The semiconductor device of claim 1, wherein the first reflector comprises an n-type semiconductor multilayer film; The red surface emitting laser device further comprises an n-type semiconductor spacer layer between the first reflecting mirror and the active layer. The red surface emitting laser device of claim 1, further comprising another spacer layer between the p-type semiconductor spacer layer and the active layer. The resonator of claim 10, wherein the active layer, the p-type semiconductor spacer layer, and the n-type semiconductor spacer layer comprise a resonator, and the resonator has an asymmetric structure in which the active layer is not located at the center of the resonator length direction of the resonator. Red surface-emitting laser element, characterized in that. The red surface emitting laser device of claim 12, wherein a thickness of the p-type semiconductor spacer layer is thicker than a thickness of the n-type semiconductor spacer layer. The red surface emitting laser device according to claim 1, wherein the resonator length of the resonator including the active layer is 1.5 or more and 4 or less. A red surface emitting laser device according to claim 1; And And a deflector for scanning by reflecting the laser light output from the laser element. 16. The apparatus of claim 15, further comprising: a photosensitive member for forming an electrostatic latent image by light deflected by the deflector; Charger; Developing machine; And An image forming apparatus comprising a fixing unit. A red surface emitting laser device according to claim 1; And And a deflector for scanning by reflecting the laser light output from the laser element. The red surface emitting laser device of claim 1, wherein the active layer comprises a plurality of active layers. First reflecting mirror; a second reflecting mirror comprising a p-type AlGaAs semiconductor multilayer film; An active layer between the first reflecting mirror and the second reflecting mirror; And And a p-type AlInP semiconductor spacer layer or a p-type AlGaInP semiconductor spacer layer having a thickness of 100 nm or more and 350 nm or less between the active layer and the second reflecting mirror. First reflecting mirror; a second reflector including a p-type semiconductor multilayer film; An active layer between the first reflecting mirror and the second reflecting mirror; And A p-type semiconductor spacer layer between the active layer and the second reflector, The conduction band edge at the endpoint of the p-type semiconductor multilayer film is lower than the conduction band edge at the endpoint of the p-type semiconductor spacer layer, The thickness of the p-type semiconductor spacer layer is 100 nm or more and 350 nm or less.

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