JP2010258134A - Method of manufacturing quantum well structure, semiconductor laser, and compound semiconductor layer, and method of controlling mbe (molecular beam epitaxy) device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a quantum well structure having a well layer with high photoluminescence intensity, a semiconductor laser, and a compound semiconductor layer with the high photoluminescence intensity, and to provide a method of controlling a molecular beam epitaxy device using the photoluminescence intensity of the compound semiconductor layer. <P>SOLUTION: The quantum well structure has the well layer consisting of InGaAs or GaInNAs, wherein an oxygen concentration of the well layer is no more than 5×10<SP>16</SP>atoms/cm<SP>3</SP>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a quantum well structure, a semiconductor laser, a compound semiconductor layer, and a method for managing the state of an MBE device.

  It is known that when a GaAs layer is grown at 350 to 450 ° C. using an MBE apparatus, oxygen is mixed into the GaAs layer (see Non-Patent Document 1).

  In addition, a method for detecting oxygen in a GaAs layer by photoluminescence measurement of the GaAs layer is known (see Non-Patent Document 2).

CH Goo et.al., "High oxygen and carbon contents in GaAsepilayers grown below a critical substrate temperature by molecular beamepitaxy", Appl. Phys. Lett., Vol. 68, No. 6, February 1996, pp.841- 843 W. J. Turner et. Al., "Luminescence of GaAs Grown in Oxygen", Journal of Applied physics vol. 34, No. 11 November 1963, pp.3274-3276

  However, the correlation between the oxygen concentration of the compound semiconductor layer and the photoluminescence intensity (PL intensity) is not known. Furthermore, in the case of InGaAs or GaInNAs different from GaAs, it is difficult to obtain a high PL intensity. If the PL intensity is low, the laser threshold of the semiconductor laser will be high.

  The present invention has been made in view of the above circumstances, a quantum well structure having a well layer with high photoluminescence intensity, a semiconductor laser, a method for producing a compound semiconductor layer with high photoluminescence intensity, and a photo of the compound semiconductor layer It aims at providing the method of managing the state of an MBE apparatus using luminescence intensity.

  In the case of GaAs, the oxygen concentration can be reduced by increasing the growth temperature. Therefore, in order to solve the above-mentioned problem, the present inventor has studied to reduce the oxygen concentration of the compound semiconductor layer made of InGaAs or GaInNAs. However, in the case of InGaAs or GaInNAs, unlike GaAs, when the growth temperature is raised, InGaAs or GaInNAs grows in an island shape (three-dimensional growth) by so-called SK mode growth. For this reason, it is difficult to reduce the oxygen concentration by increasing the growth temperature.

  As a result of intensive studies, the present inventor has found that the oxygen concentration in InGaAs or GaInNAs can be reduced by heat-treating at least one of the chamber and the raw material of the MBE apparatus.

The quantum well structure of the present invention has a well layer made of InGaAs or GaInNAs, and the oxygen concentration of the well layer is 5 × 10 ¹⁶ atoms / cm ³ or less.

  In the quantum well structure of the present invention, the photoluminescence intensity of the well layer can be increased. The composition ratio of InGaAs and GaInNAs is not particularly limited. The oxygen concentration is measured by, for example, secondary ion mass spectrometry (SIMS).

The semiconductor laser of the present invention has a quantum well structure having a well layer made of InGaAs or GaInNAs, and the well layer has an oxygen concentration of 5 × 10 ¹⁶ atoms / cm ³ or less. In the semiconductor laser of the present invention, the laser threshold can be lowered because the photoluminescence intensity of the well layer is high.

A method of manufacturing a compound semiconductor layer of the present invention is a method of manufacturing a compound semiconductor layer made of InGaAs or GaInNAs by supplying a raw material into a chamber of an MBE apparatus, the chamber of the MBE apparatus and the raw material And a growth step of growing the compound semiconductor layer at 460 ° C. or lower after the heat treatment step, wherein the oxygen concentration of the compound semiconductor layer is 5 × 10 ¹⁶ atoms / cm ^The heat treatment step is performed so as to be ³ or less.

  In the method of manufacturing a compound semiconductor layer according to the present invention, at least one of the chamber and the raw material of the MBE apparatus is heat-treated, thereby removing oxygen attached to the chamber of the MBE apparatus and oxides formed on the surface of the raw material. be able to. As a result, it becomes difficult for oxygen to be mixed into the compound semiconductor layer in the growth process. Therefore, a compound semiconductor layer with high photoluminescence intensity can be manufactured. In addition, since the compound semiconductor layer is grown at a low temperature of 460 ° C. or lower, InGaAs or GaInNAs can be prevented from growing in an island shape.

In the heat treatment step, the oxygen concentration of the compound semiconductor layer can be controlled by adjusting the heat treatment temperature, the heat treatment time, and the like. For example, the oxygen concentration of the compound semiconductor layer can be reduced by increasing the heat treatment temperature and lengthening the heat treatment time. In the method for producing the compound semiconductor layer of the present invention, the heat treatment step is performed so that the oxygen concentration of the compound semiconductor layer is 5 × 10 ¹⁶ atoms / cm ³ or less.

  The method for managing the state of the MBE device of the present invention includes a growth step of growing a compound semiconductor layer made of InGaAs or GaInNAs using the MBE device, a measurement step of measuring the photoluminescence intensity of the compound semiconductor layer, And a determination step of determining the state of the MBE device using photoluminescence intensity.

  In the method for managing the state of the MBE apparatus according to the present invention, since the photoluminescence intensity of the compound semiconductor layer is used, the state of the MBE apparatus can be managed easily and inexpensively. In the determination step, for example, when the photoluminescence intensity is equal to or higher than a predetermined value, it is determined that the state of the MBE apparatus is good, and when it is less than the predetermined value, it is determined that the state of the MBE apparatus is defective. Can do. Alternatively, a correlation between the photoluminescence intensity and the oxygen concentration may be obtained in advance, and the oxygen concentration may be calculated using the measured photoluminescence intensity using the correlation. In that case, when the oxygen concentration is equal to or lower than the predetermined value, it is determined that the state of the MBE apparatus is good, and when it exceeds the predetermined value, it can be determined that the state of the MBE apparatus is defective.

  Here, the state of the MBE apparatus being good means that oxygen adhering to the chamber of the MBE apparatus, oxides formed on the surface of the raw material, and the like are appropriately removed. In addition, the state of the MBE apparatus being defective means that oxygen attached to the chamber of the MBE apparatus, oxide formed on the surface of the raw material, or the like is not properly removed.

  According to the present invention, a quantum well structure having a well layer with high photoluminescence intensity, a semiconductor laser, a method for producing a compound semiconductor layer with high photoluminescence intensity, and the state of the MBE apparatus using the photoluminescence intensity of the compound semiconductor layer A method of managing is provided.

It is sectional drawing which shows typically a semiconductor laser provided with the quantum well structure which concerns on embodiment. It is a figure which shows typically the MBE apparatus used suitably for the method of manufacturing the compound semiconductor layer which concerns on embodiment. It is a flowchart which shows each process of the method of manufacturing the compound semiconductor layer which concerns on embodiment, and the method of managing the state of a MBE apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

FIG. 1 is a cross-sectional view schematically showing a semiconductor laser having a quantum well structure according to an embodiment. A semiconductor laser 10 shown in FIG. 1 includes a GaAs substrate 2, a GaAs layer 4, a GaInP layer 6, a quantum well structure 8, a GaInP layer 10 and a GaAs layer 12 in this order. The GaAs layer 12 serving as a contact layer is provided on the first region on the surface of the GaInP layer 10. A SiO ₂ layer 14 is provided on the second region surrounding the first region on the surface of the GaInP layer 10. A p-electrode 16 is formed on the GaAs layer 12 and the SiO ₂ layer 14. An n-electrode 18 is formed on the back surface of the GaAs substrate 2. The semiconductor laser 10 is an edge-emitting laser, for example, and is preferably used for communication purposes.

The quantum well structure 8 includes well layers 22 and barrier layers 20 that are alternately stacked. The well layer 22 is made of InGaAs or GaInNAs. The In composition is preferably 30% or more, and the N composition is preferably 0.5 to 1%. Oxygen concentration of the well layer 22 is greater than 0atoms / cm ^3, 5 × is at ¹⁰ 16 atoms / cm ³ or less, or 2 × ¹⁰ 16 atoms / cm ³ or less. The barrier layer 20 is made of, for example, GaAs. The quantum well structure 8 may be a single quantum well structure (SQW) having one well layer 22 or a multiple quantum well structure (MQW) having a plurality of well layers 22. The quantum well structure 8 is non-doped. The film thickness of the well layer 22 is, for example, 7 nm. The film thickness of the barrier layer 20 is, for example, 140 nm. The thickness of the barrier layer 20 disposed between the plurality of well layers 22 is, for example, 10 nm.

The GaInP layer 10 and the GaAs layer 12 are doped with Zn, for example. The carrier density of the GaInP layer 10 is, for example, 7 × 10 ¹⁷ cm ⁻³ . The film thickness of the GaInP layer 10 is, for example, 1500 nm. The carrier density of the GaAs layer 12 is, for example, 20 × 10 ¹⁷ cm ⁻³ . The film thickness of the GaAs layer 12 is, for example, 200 nm.

The GaInP layer 6 and the GaAs layer 4 are doped with, for example, Si. The carrier density of the GaInP layer 6 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the GaInP layer 6 is, for example, 1400 nm. The carrier density of the GaAs layer 4 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The thickness of the GaAs layer 4 is, for example, 200 nm.

  In the quantum well structure 8 of the present embodiment, since the oxygen concentration of the well layer 22 is low, the photoluminescence intensity (PL intensity) of the well layer 22 can be increased. Further, in the semiconductor laser 10, since the PL intensity of the well layer 22 is high, the laser threshold can be lowered.

FIG. 2 is a diagram schematically showing an MBE apparatus (molecular beam epitaxy apparatus) suitably used in the method for manufacturing the compound semiconductor layer according to the embodiment. The MBE apparatus 50 shown in FIG. 2 includes a chamber 52 and a substrate holder 54 disposed in the chamber 52. The inside of the chamber 52 can be maintained at an ultrahigh vacuum of, for example, 1 × 10 ⁻¹⁰ Torr or less. The substrate holder 54 is connected to a rotation mechanism 58 disposed outside the chamber 52 via a holding unit 56. The rotation mechanism 58 is a manipulator, for example. The substrate holder 54 is rotated by the rotation mechanism 58. A substrate such as the GaAs substrate 2 is placed on the substrate holder 54.

A Ga cell 60, an In cell 62, an As cell 64, and an N radical gun 66 are connected to the chamber 52. An N ₂ gas source 68 is connected to the N radical gun 66 through a pipe 77. In the N radical gun 66, N radicals are generated from N ₂ gas by RF plasma. Ga, In, As, and N radicals are supplied into the chamber 52 from the Ga cell 60, In cell 62, As cell 64, and N radical gun 66, respectively. As a result, a compound semiconductor layer such as the well layer 22 is formed on the substrate. An exhaust pump 72 is connected to the chamber 52. The gas in the chamber 52 is exhausted by the exhaust pump 72.

  The chamber 52 is covered with a heat insulating material 74 such as a heat insulating panel or a heat insulating jacket. A heater 76 for heating the chamber 52 is disposed between the chamber 52 and the heat insulating material 74. A heater 78 that heats the Ga cell 60 is disposed between the Ga cell 60 and the heat insulating material 74. A heater 80 that heats the As cell 64 is disposed between the As cell 64 and the heat insulating material 74.

FIG. 3 is a flowchart showing each step of the method for manufacturing the compound semiconductor layer and the method for managing the state of the MBE apparatus according to the embodiment.
(Heat treatment process)

First, the chamber 52 of the MBE apparatus 50 is heat-treated (step S10). For example, the chamber 52 can be heat-treated by using the heater 76 while exhausting by the exhaust pump 72. The heat treatment temperature is, for example, 100 to 200 ° C. The heat treatment time is, for example, 1 to 3 weeks. The heat treatment temperature and the heat treatment time are appropriately adjusted according to the size and shape of the chamber 52. By heat-treating the chamber 52, the gas adsorbed on the inner wall of the chamber 52 can be removed. Here, since the degree of vacuum of the chamber 52 tends to decrease during the temperature increase due to the release of the adsorbed gas, the temperature increase rate is reduced so that the pressure in the chamber 52 becomes 1 × 10 ⁻⁷ Torr or less. It is preferable.

Next, a raw material such as Ga cell 60 or As cell 64 is heat-treated (step S12). For example, the Ga cell 60 or the As cell 64 can be heat-treated by using the heater 78 or the heater 80 while exhausting with the exhaust pump 72. In the case of the Ga cell 60, the heat treatment temperature is, for example, 1100 ° C., and the heat treatment time is, for example, 10 hours or more. In the case of the As cell 64, the heat treatment temperature is, for example, 300 ° C., and the heat treatment time is, for example, 10 hours or more. The heat treatment temperature and the heat treatment time are appropriately adjusted according to the amount of raw material supplied. By heat-treating the raw material such as the Ga cell 60 or the As cell 64, oxides and the like formed on the surface of the raw material can be removed. Here, since the degree of vacuum in the chamber 52 tends to decrease during the temperature increase due to the gas release from the raw material, the temperature increase rate is reduced so that the pressure in the chamber 52 becomes 1 × 10 ⁻⁷ Torr or less. It is preferable to do.
(Growth process)

  Next, by supplying raw materials such as Ga, In, As, and N radicals into the chamber 52 of the MBE apparatus 50, the well layer 22 (compound semiconductor layer) made of InGaAs or GaInNAs is formed at 460 ° C. or less at the GaAs substrate 2 And so on (step S14). The growth temperature of the well layer 22 is preferably 400 ° C. or lower. Note that the GaAs layer 4, the GaInP layer 6, and the barrier layer 20 may be grown between the heat treatment step and the growth step.

  A compound semiconductor layer can be manufactured through steps S10, S12, and S14 in this order. In addition, although it is not necessary to implement any one of process S10 and S12, it is preferable to implement both.

  In the method of manufacturing the compound semiconductor layer according to this embodiment, at least one of the chamber 52 and the raw material of the MBE apparatus 50 is heat-treated to thereby oxidize the oxygen deposited on the chamber 52 of the MBE apparatus 50 and the surface of the raw material. Things can be removed. As a result, it becomes difficult for oxygen to be mixed into the well layer 22 in the growth step S14. Therefore, the well layer 22 with high PL strength can be manufactured. Examples of oxygen attached to the chamber 52 include arsenic oxide formed by oxidizing As attached to the inner wall of the chamber 52 when the chamber 52 is opened to the atmosphere for maintenance.

  Moreover, since the well layer 22 is grown at a low temperature of 460 ° C. or lower, it is possible to prevent InGaAs or GaInNAs from growing in an island shape. From the viewpoint of suppressing island-like growth, it is preferable to lower the growth temperature as the In composition of the well layer 22 is higher.

In the heat treatment step, the oxygen concentration of the well layer 22 can be controlled by adjusting the heat treatment temperature, the heat treatment time, and the like. For example, the oxygen concentration of the well layer 22 can be reduced by increasing the heat treatment temperature and lengthening the heat treatment time. In the method for manufacturing the compound semiconductor layer of the present embodiment, the heat treatment step is performed so that the oxygen concentration of the well layer 22 is 5 × 10 ¹⁶ atoms / cm ³ or less.
(Measurement process)

Next, the PL intensity of the well layer 22 is measured (step S16). The PL intensity is measured at room temperature (for example, 0 to 30 ° C.). One PL intensity measurement is completed in about several minutes. The PL intensity measurement time is much shorter than the SIMS measurement time. Further, the PL intensity measuring device is less expensive than the SIMS measuring device.
(Judgment process)

  Next, the state of the MBE apparatus 50 is determined using the PL intensity as an index (step S18). For example, when the PL intensity is a predetermined value (for example, 4) or more, it is determined that the state of the MBE apparatus 50 (the concentration of oxygen attached to the chamber 52 and the raw material) is good. When the PL intensity is less than a predetermined value (for example, 4), it is determined that the state of the MBE apparatus 50 (the concentration of oxygen attached to the chamber 52 or the raw material) is defective. In that case, the process returns to step S10.

Alternatively, a correlation between PL intensity and oxygen concentration may be obtained in advance by PL intensity measurement and SIMS measurement, and the oxygen concentration may be calculated using the measured PL intensity using the correlation. In that case, when the oxygen concentration is a predetermined value (for example, 5 × 10 ¹⁶ atoms / cm ³ ) or less, it is determined that the state of the MBE apparatus 50 is good. When the oxygen concentration exceeds a predetermined value (for example, 5 × 10 ¹⁶ atoms / cm ³ ), it is determined that the state of the MBE apparatus 50 is defective. In that case, the process returns to step S10. As the oxygen concentration decreases, the PL intensity increases.

  By sequentially performing steps S14, S16, and S18, it is possible to manage the MBE device 50 so that the state is good.

  In the method for managing the state of the MBE apparatus according to this embodiment, the PL intensity of the well layer 22 is used, so that the state of the MBE apparatus 50 can be managed easily and inexpensively.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an experiment example, an Example, and a comparative example, this invention is not limited to a following example.
(Experimental example 1)

The chamber of the MBE apparatus was heat-treated at 200 ° C. for 1 week (baking). Thereafter, a GaAs layer was grown at 440 ° C. The growth rate was 0.4 μm / h. The oxygen concentration of the obtained GaAs layer was 4.4 × 10 ¹⁶ atoms / cm ³ .
(Experimental example 2)

The experiment was performed in the same manner as in Experimental Example 1 except that the GaAs layer was grown at 460 ° C. The oxygen concentration of the GaAs layer was 2.4 × 10 ¹⁶ atoms / cm ³ .
(Experimental example 3)

The experiment was performed in the same manner as in Experimental Example 1 except that the GaAs layer was grown at 470 ° C. The oxygen concentration of the GaAs layer was 1.4 × 10 ¹⁶ atoms / cm ³ .
(Experimental example 4)

The experiment was performed in the same manner as in Experimental Example 1 except that the GaAs layer was grown at 560 ° C. The oxygen concentration of the GaAs layer was 1.3 × 10 ¹⁶ atoms / cm ³ .
(Experimental example 5)

The experiment was performed in the same manner as in Experimental Example 1 except that the InGaAs layer was grown at 440 ° C. The oxygen concentration of the InGaAs layer was 1.4 × 10 ¹⁷ atoms / cm ³ .
(Experimental example 6)

The experiment was performed in the same manner as in Experimental Example 1 except that the GaInNAs layer was grown at 440 ° C. The oxygen concentration of the GaInNAs layer was 8.6 × 10 ¹⁷ atoms / cm ³ .
(Evaluation results)

  From Experimental Examples 1 to 4, it has been found that in GaAs, the oxygen concentration decreases as the growth temperature increases. However, with InGaAs and GaInNAs, it is difficult to increase the growth temperature from the viewpoint of suppressing three-dimensional growth. From Experimental Examples 5 and 6, it was found that when InGaAs or GaInNAs was grown at 440 ° C., the oxygen concentration increased.

  In addition, from Experimental Examples 1, 5 and 6, it was found that the GaInNAs had a higher oxygen concentration than GaAs or InGaAs. This is presumably because oxygen present in the chamber is activated by N radicals, so that the reactivity increases and the adhesion coefficient increases.

Based on the results of Experimental Examples 1 to 6, the following experiments were performed.
Example 1

  The chamber of the MBE apparatus was heat-treated at 200 ° C. for 3 weeks (baking). Then, the new Ga cell exchanged by maintenance was heat-treated at 1100 ° C. for 11 hours (degassing). Furthermore, a single quantum well structure having an InGaAs layer as a well layer was produced.

Specifically, after introducing a GaAs substrate doped with Si into the chamber of the MBE apparatus, the GaAs substrate temperature was raised to 600 ° C. in an As irradiation atmosphere. As a result, the native oxide on the surface of the GaAs substrate was removed. Thereafter, a non-doped GaAs layer having a thickness of 0.2 μm was grown on the GaAs substrate. Thereafter, the growth temperature was lowered to 400 ° C., and then an InGaAs layer having a thickness of about 7 nm was grown. Thereafter, a GaAs layer having a thickness of 5 nm was grown, and then the growth temperature was raised to 550 ° C. Further, a GaAs layer having a thickness of 0.1 μm was grown.
(Example 2)

A single quantum well structure of Example 2 was produced in the same manner as in Example 1 except that the Ga cell was heat-treated at 1100 ° C. for 10 hours.
(Comparative Example 1)

A single quantum well structure of Comparative Example 1 was produced in the same manner as in Example 1 except that the Ga cell was heat-treated at 1100 ° C. for 5 hours.
(Comparative Example 2)

A single quantum well structure of Comparative Example 2 was produced in the same manner as in Example 1 except that the Ga cell was heat-treated at 1100 ° C. for 1 hour.
(Evaluation results)

The oxygen concentrations of the InGaAs layers (well layers) of Examples 1-2 and Comparative Examples 1-2 were measured by SIMS, respectively. The detection lower limit (background) of SIMS was 1 × 10 ¹⁶ to 2 × 10 ¹⁶ atoms / cm ³ . The background varies depending on the SIMS device state. The results are shown in Table 1.

Furthermore, the PL intensity | strength of InGaAs layer (well layer) of Examples 1-2 and Comparative Examples 1-2 was measured at room temperature, respectively. The PL intensity was a relative value based on the standard sample. When a semiconductor laser was manufactured using an InGaAs layer having a PL intensity of 1, an InGaAs layer having a threshold current density of 500 A / cm ² or less was used as a standard sample. The results are shown in Table 1.

The oxygen concentration in Example 1 was at the background level. Further, the PL intensity (4.6) of Example 1 and the PL intensity (5.3) of Example 2 were within the range of variations and were at the same level.
(Comparative Example 3)

After performing maintenance for exchanging all of the cryopump for exhaust and the cell shutter with new ones, the chamber of the MBE apparatus was heated at 200 ° C. for 3 weeks (baking). Thereafter, the Ga cell was heat-treated at 200 ° C. in the MBE apparatus for 1 hour (degassing). Thereafter, an InGaAs layer was grown at 440 ° C. The PL intensity of the InGaAs layer was 0.46. The oxygen concentration of the InGaAs layer was 2.0 × 10 ¹⁷ atoms / cm ³ .
(Example 3)

An InGaAs layer was grown in the same manner as in Comparative Example 3 except that the Ga cell was heat treated at 1000 ° C. for 3 hours. The PL intensity of the InGaAs layer was 5. The oxygen concentration of the InGaAs layer was 3.0 × 10 ¹⁶ atoms / cm ³ . Note that the time required for the heat treatment of the Ga cell is not necessarily constant depending on the lot of the raw material and the state of the chamber.

  DESCRIPTION OF SYMBOLS 8 ... Quantum well structure, 10 ... Semiconductor laser, 22 ... Well layer (compound semiconductor layer), 50 ... MBE apparatus, 52 ... Chamber, 60 ... Ga cell (raw material), 64 ... As cell (raw material).

Claims (4)

Having a well layer made of InGaAs or GaInNAs,
A quantum well structure, wherein the well layer has an oxygen concentration of 5 × 10 ¹⁶ atoms / cm ³ or less. A quantum well structure having a well layer made of InGaAs or GaInNAs,
A semiconductor laser, wherein the well layer has an oxygen concentration of 5 × 10 ¹⁶ atoms / cm ³ or less. A method of manufacturing a compound semiconductor layer made of InGaAs or GaInNAs by supplying a raw material into a chamber of an MBE apparatus,
A heat treatment step of heat treating at least one of the chamber and the raw material of the MBE apparatus;
A growth step of growing the compound semiconductor layer at 460 ° C. or lower after the heat treatment step;
Including
The method of performing the said heat treatment process so that the oxygen concentration of the said compound semiconductor layer may be 5 * 10 < ¹⁶ > atoms / cm < ³ > or less. A growth step of growing a compound semiconductor layer made of InGaAs or GaInNAs using an MBE apparatus;
A measuring step of measuring the photoluminescence intensity of the compound semiconductor layer;
A determination step of determining the state of the MBE device using the photoluminescence intensity;
A method for managing the state of an MBE device.

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