MBE Components, Valved GaP Compound Source VGCS

VGCS

Valved GaP Compound Source

VGCS 100-420
  • Produces pure P2 species (P2/P4 > 150)

  • Fast, stable and reproducible flux control

  • Large crucible capacity of 420 cm3

  • Safe cell loading and operation

  • Reliable large cross section cone valve

  • No hot cracker zone

  • Injector length and flux distribution adjustable

    to fit most MBE systems

 VGCS 100-420 valved GaP compound source on DN100 CF (O.D. 6") mounting flange with 420 cm³ crucible

Download IconData Sheet


The Valved GaP Compound Source VGCS is a high purity P2-source, based on the decomposition of high purity GaP. The concept is derived from our DECO effusion cells to which a mechanical valve mechanism is added for rapid beam flux control.

Full MBE compatibility is reached by the integrated Gallium-Trapping-System, the integrated water cooling as well as the use of high purity inert materials such as pyrolytic boron nitride for all parts in the direct phosphorus path.

In contrast to sources using elemental phosphorus only minor amounts of white phosphorus are formed within the cell and the formation of white phosphorus within the MBE chamber is significantly reduced due to the direct formation of P2 species from the decomposition of single crystal GaP chunks with purity 6N-7N.
Operation of the mechanical valve unit shows fast, stable and reproducible flux control. Together with our valve controller an easy handling and integration to your MBE system is provided.

The design of the valve mechanism is schematically illustrated on the right side. It provides a large cross section opening which allows very good pumping of the GaP reservoir. The robust wide angle valve design effectively elimitates the chance of locking, which is a frequently observed problem for needle valves.
The VGCS has proven to be a very reliable P2 source in the field and is compatible to commenly used industrial and research MBE systems.


VGCS valve design

Schematic illustration of the VGCS valve design


The figure on the right hand side shows the beam equivalent pressure (BEP) at the substrate position measured as a function of the valve position.
The Motorized Valve Control Unit MVCU is designed for operating the valve of a valved source with a servo motor drive. Manual or remote control with 0-10 V analogue input signal is possible. The display indicates the linear position of the valve from 0 - 7.99 mm from fully closed to fully open position. The servo motor drive has a resolution of 0.01 mm per step and a high motor speed of 10 mm/s. The automatic zero calibration guarantees a highly reliable and reproducible operation of the valve unit.

BEP vs. valve position

SIMS concentration vs. depth High purity of GaInP layers grown on GaAs is demonstrated by SIMS measurements (see figure on the left).
The contamination of the GaInP layer with oxygen and carbon is below the detection limit of about 5x1016 cm-3 using highest purity single crystal GaP source material. The high performance of the phosphorus source allows growth of high quality GaInP/AlGaInP laser diodes or other P-compounds.


BEP vs. time BEP vs. time
BEP vs. time, with the valve on and off.
The P2 pressure can be switched by about two orders of magnitude.
BEP during ramp up of the reservoir temperature from 800 to 1000°C.
The flux can be adjusted within minutes, due to the high reservoir temperature.

Comparison with other Elemental Phosphorus Cells

Valved Elemental Phosphorus Cracker

Valved GaP Compound Source (VGCS)

principle

  • complicated 2-reservoir system
  • convertion of red P to white P
  • separate high temperature cracker for P2 forming
  • overpressure in reservoir possible and boost problem
  • single reservoir GaP sublimation
  • natural P2 source
  • no high temperature cracking needed
  • efficient Ga trapping
  • no pressure boost due to recombination of excess P back to GaP in the reservoir

flux control

  • mechanical valve control
  • instanteous shut off
  • mechanical valve control
  • instanteous shut off

source material

  • red P chunk, 6N-7N purity
  • crystalline GaP chunk, 6N-7N purity

handling + safety

  • elemental phosphorus
  • reload delicate with lots of white P everywhere
  • very high risk of fire
  • stable semiconductor crystals
  • easy to clean and handle
  • no white P in the reservoir
  • reloading easy with much lower risk of fire



Application

The VGCS is designed for growth of phosphide compounds in III-V-MBE. It has been readily approved in industrial applications. The fast and reproducible flux control using a valve allows the growth of phosphide-arsenide heterostructures with very sharp interfaces like quantum wells and superlattices. It is perfectly suited for applications in HEMTs, HBTs, GaAlInP laser diodes and other devices. Also GaInP/InP quantum dot lasers have been prepared. Moreover, very good results for pseudomorphic high electron mobility transistors have been achieved.
The large crucible size makes the VGCS well suited for MBE research and production systems.

The right picture shows red light emission from a GaAs/GaInP/AlInP laser diode grown and processed at the Max Planck Institute for Solid State Research in Stuttgart


Red light emission

Very sharp transitions of P are achieved by application of VGCS and VACS sources at one deposition run. 300nm GaInP are deposited on a GaAs buffer layer on a (100) GaAs substrate. Due to the fast flux control properties of the valve unit P is sharply reduced on the GaInP/GaAs interface as demonstrated by the SIMS measurement on the right.
In return, the As concentration in the GaInP layer is at its detection limit and three orders of magnitude below the GaAs level.

SIMS measurement


References

There are several publications for GaP decomposition source and valved GaP compound source. Please have a look at section References / List of Publications. 


Technical Data

Filament type 2 separate heater-circuits (cell / valve)
Thermocouple W5%Re/W26%Re (type C); 2 thermocouples (cell/valve)
Operating temperature cell crucible: 800-950°C; valve: 350°C
Outgassing temperature cell crucible: 1300°C; valve: 500°C
Bakeout temperature 250°C
Cooling integrated water cooling shrouds
Crucibles 420 cm³
Flux control
integrated valve unit
Valve control servo motor drive with control unit MVCU



Dimensions

Schematic drawing VGCS Schematic drawing of the Valved GaP compound Source VGCS

(drawing shows
VGCS 100-420 with VADAP adapter)



Specific data

For general information on CF mounting flanges see Flange and Gasket dimensions.

images/header_nominal_capacity.gif
[cm3] [mm] / [mm] [W] / [A] Product code
VGCS 100*- 420**- LxxD57 cell: 600 / 12
injector: 150 / 7
cell: PS 70-22-C
injector: PS 30-10-C
* other mounting flange diameters feasible in combination with VADP adapter flanges (on request)
** other capacities on request
*** specify UHV length L with order

Product code:

e.g. VGCS 100-420-L300D57

is a valved GaP compound souce on DN100 CF flange with 420cm³ crucible and UHV-length 300mm.