Method and system for vertical gradient freeze 8 inch gallium arsenide substrates

Abstract

Methods and wafers for vertical gradient freeze 8 inch gallium arsenide (GaAs) substrates. In disclosed examples, vertical gradient freeze systems for forming gallium arsenide (GaAs) substrates having silicon as a dopant, the system includes a crucible to contain a GaAs liquid melt and seed material during a formation process; one or more heating coils arranged in a plurality of heating zones; and a pedestal to move relative to the crucible, the system operable to control heating of the plurality of heating zones and movement of the pedestal to form a single crystal GaAs substrate.

What is claimed is: 
     
         1 . A vertical gradient freeze system for forming gallium arsenide (GaAs) 8 inch substrates having silicon as a dopant, the system comprising:
 a crucible to contain a GaAs liquid melt and seed material during a formation process;   one or more heating coils arranged in a plurality of heating zones; and   a pedestal to move relative to the crucible, the system operable to control heating of the plurality of heating zones and movement of the pedestal to form a single crystal GaAs substrate.   
     
     
         2 . The system according to  claim 1 , further comprising an ampule to support the crucible. 
     
     
         3 . The system according to  claim 1 , wherein the pedestal is operable to move the crucible relative to the heating coils. 
     
     
         4 . The system according to  claim 1 , wherein the pedestal is operable to rotate relative to the heating coils. 
     
     
         5 . The system according to  claim 1 , wherein the pedestal is operable to move vertically relative to the heating coils. 
     
     
         6 . The system according to  claim 1 , wherein the heating coils are operable to activate or the pedestal is operable to move to control a shape of an interface between the GaAs liquid melt and crystals to achieve low etch pit density (EPD). 
     
     
         7 . The system according to  claim 6 , wherein the shape is concave to the GaAs liquid melt. 
     
     
         8 . The system according to  claim 7 , wherein the shape of the interface is between 5-20 mm concave, such that the center is 5-20 mm lower than an edge of the substrate. 
     
     
         9 . The system according to  claim 1 , wherein a boron trioxide B 2 O 3  layer is placed as an encapsulant on the GaAs liquid melt to reduce loss of crystal growth material. 
     
     
         10 . The system according to  claim 1 , wherein the heating coils are operable to activate or the pedestal is operable to move to control a crystallization velocity as controlled by the cooling rate may be configured to a range from 0.1-1.0 degrees C./hour. 
     
     
         11 . The system according to  claim 1 , wherein the heating coils are operable to activate or the pedestal is operable to move to control a temperature gradient at the GaAs liquid melt/crystal interface may be configured to be between 1-10 degree C./cm. 
     
     
         12 . The system according to  claim 1 , further comprising insulation placed on or within the pedestal to promote radial heat flux inward during growth or heat removal during post-growth process and cooling. 
     
     
         13 . The system according to  claim 1 , wherein one or more electronic or optoelectronic devices are formed on a first surface of the surface. 
     
     
         14 . The system according to  claim 13 , wherein the electronic or optoelectronic devices are one or more of a light-emitting diodes (LEDs), lasers, heterojunction bipolar transistors (HBTs), and pseudo-morphic high-electron mobility transistors (pHEMTs). 
     
     
         15 . The system according to  claim 13 , wherein the substrate is diced into a plurality of die, such that optical signals from an optoelectronic device of the electronic or optoelectronic devices on a first side of the substrate are communicated out a second side of the substrate opposite to the first side. 
     
     
         16 . The system according to  claim 1 , wherein the substrate has an etch pit density of less than 200 cm-2. 
     
     
         17 . The system according to  claim 1 , wherein the substrate has a dopant concentration of 1×10 19  cm −3  or greater. 
     
     
         18 . The system according to  claim 1 , wherein the substrate has a thickness of 300 μm or greater. 
     
     
         19 . A method for forming single crystal gallium arsenide substrates, the method comprising:
 sealing charge material comprising polycrystalline gallium arsenide (GaAs) seed crystal, B 2 O 3  encapsulant, and carbon in a crucible;   sealing the crucible in a quartz ampoule;   performing a vertical gradient freeze crystal growth process by heating the ampoule using a multi-zone heating system to progressively melt the charge material until a portion of the seed crystal is melted;   moving a pedestal relative to the crucible, the system operable to control heating of the multi-zone heating system and movement of the pedestal; and   implementing controlled cooling of the multi-zone heating system during growth from the partially melted seed to form a single crystal 8 inch GaAs substrate.   
     
     
         20 . The method according to  claim 19 , further comprising applying a temperature gradient of between 1 and 8 C/cm at a melt-crystal interface. 
     
     
         21 . The method according to  claim 19 , further comprising controlling a shape of the interface to be concave to the melt utilizing cooling rates in the multi-zone heating system to form a solidified gallium arsenide crystal. 
     
     
         22 . The system according to  claim 21 , wherein the shape of the interface is between 5-20 mm concave, such that the center is 5-20 mm lower than an edge of the substrate. 
     
     
         23 . The method according to  claim 19 , wherein moving the pedestal moves the crucible relative to the multi-zone heating system. 
     
     
         24 . The method according to  claim 19 , wherein moving the pedestal rotates the crucible relative to the multi-zone heating system. 
     
     
         25 . The method according to  claim 19 , wherein moving the pedestal moves the crucible vertically relative to the multi-zone heating system. 
     
     
         26 . The method according to  claim 19 , further comprising controlling the multi-zone heating system or the pedestal movement to control a crystallization velocity as controlled by the cooling rate may be configured to a range from 0.1-2.0 degrees C./hour. 
     
     
         27 . The method according to  claim 19 , further comprising forming one or more electronic or optoelectronic devices on a first surface of the substrate. 
     
     
         28 . The method according to  claim 27 , wherein the electronic or optoelectronic devices are one or more of a light-emitting diodes (LEDs), lasers, heterojunction bipolar transistors (HBTs), and pseudo-morphic high-electron mobility transistors (pHEMTs). 
     
     
         29 . The method according to  claim 19 , comprising evacuating the crucible before sealing it into the quartz ampoule. 
     
     
         30 . The method according to  claim 19 , comprising cooling the solidified charge material at rates of 0.5 to 5 C/h, 1 to 10 C/h and 5 to 20 C/h for different heating zones of the multi-zone heating system for the first 300 C, and then at rates of 20-50 C/h to room temperature.